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VARIOUS     SPECTRA 


FIRST   PRINCIPLES 


OF 


CHEMISTRY 


BY 


RAYMOND  B.   BROWNLEE  ROBERT  W.  FULLER 

•     STUYVESANT   HIGH    SCHOOL  STUYVESANT   HIGH   SCHOOL 

WILLIAM  J.  HANCOCK  MICHAEL  D.  SOHON 

ERASMUS   HALL   HIGH   SCHOOL  MORRIS   HIGH   SCHOOL 

JESSE  E.  WHITSIT 

DE  WITT  CLINTON   HIGH   SCHOOL 
ALL  OF   NEW  YORK  CITY 


Hefateefc  Xfcition 


ALLYN    AND    BACON 

Boston  Neto  gork  Cjjicago 


B76 


COPYRIGHT,  1907  AND  1915,  BY  RAYMOND  B.   BROWNLEE 
ROBERT  W.   FULLER.  WILLIAM  J.   HANCOCK 
MICHAEL  D.  SOHON.  AND  JESSE  E.  WHITSIT. 
K  I  k.\ 


TDI 


Nortooob 

J.  8.  Cashing  Co.  —  Berwick  &  Smith  Co. 
Norwood,  Mass.,  U.S.A. 


FROM  THE   PREFACE  TO  THE   FIRST 
EDITION 

IN  selecting  their  material  for  this  book,  the  authors  have 
been  governed  wholly  by  what  they  considered  of  intrinsic1 
value  to  the  elementary  student,  without  reference  to  its  tra- 
ditional place  in  a  text-book.  This  has  led  to  the  omission  of 
some  subjects  commonly  found  in  books  for  beginners.  To 
the  subjects  selected  they  have  striven  to  give  a  discussion 
simple  enough  to  be  readily  comprehended  by  the  beginner, 
and  complete  enough  to  furnish  him  with  a  clear  idea  of  the 
underlying  principles  of  Chemistry  and  a  definite  knowledge 
of  its  more  important  facts.  * 

The  experimental  determination  of  chemical  facts  is,  then, 
emphasized  from  the  first.  When  sufficient  facts  have  been 
given  to  make  explanation  necessary,  the  generalizations  of 
the  science  have  been  introduced.  In  some  of  the  theoretical 
chapters,  particularly  those  on  solution  and  ionization,  it  may 
be  advisable  to  omit  certain  portions  at  first  and  to  take  them 
up  afterwards  as  need  arises. 

The  authors  have  attempted  to  bring  out  the  fundamental 
principles  first  by  a  simple  statement,  which  is  later  developed 
and  driven  home  by  illustrations,  exercises,  and  problems,  all 
designed  to  stimulate  the  pupil  to  think  for  himself,  and  con- 
stantly to  connect  his  new  facts  with  the  facts  and  principles 
already  learned. 

In  order  to  give  the  pupil  some  idea  of  the  great  commercial 
importance  of  Chemistry,  a  number  of  typical  manufacturing 

«i" 


iV  PREFACE   TO   THE  FIRST  EDITION 

processes  have  been  described  and  illustrated.  Where  a  sub- 
stance is  manufactured  in  several  ways,  the  authors  have  tried 
to  avoid  confusion  by  giving  a  description  of  one  process  only, 
selecting  the  one  which  they  believe  is,  or  will  become,  most 
extensively  used  in  this  country.  The  commercial  production 
of  copper,  aluminum,  iron,  and  carborundum  has  been  described 
somewhat  in  detail,  for  these  are  notable  examples  of  modern 
chemical  processes. 

NEW  YORK,  August,  1907. 


PREFACE  TO   REVISED   EDITION 

• 

IN  the  preparation  of  the  Revised  Edition,  an  attempt  has 
been  made  to  rid  the  text  of  all  material  that  has  become 
obsolete,  or  that  has  proved  unadapted  to  a  first  course  in 
Chemistry.  The  general  spirit  and  the  method  of  the  book, 
however,  have  been  kept  unchanged.  Many  paragraphs  have 
been  recast,  in  order  to  make  every  statement  as  lucid  as  pos- 
sible. A  chapter  on  chemical  equilibrium  and  one  on  radio- 
activity have  been  added ;  the  one  on  the  ground  that  it 
represents  a  principle  that  is  fundamental  in  the  science,  the 
other  because  of  the  unusual  interest  that  attaches  to  the 
subject. 

Among  other  changes  that  will  be  noted  in  the  book  are  the 
extension  of  the  treatments  of  nomenclature  and  chemical  cal- 
culations, the  addition  of  a  description  of  the  lead  chamber 
process  for  sulphuric  acid,  an  increase  in  the  number  of  il- 
lustrations, and  the  substitution  of  many  new  cuts  for  the 
old.  As  in  the  first  edition,  much  attention  has  been  paid 
to  manufacturing  processes,  in  accordance  with  the  authors' 
beliefs  that  many  chemical  principles  are  best  learned  through 
their  practical  applications,  and  that  a  student  should  get  a 
very  large  amount  of  practical  information  in  his  first  course 
in  chemistry.  New  processes  have  been  introduced,  and  for- 
mer descriptions  have  been  modified  to  agree  with  present 
practice. 

The  thanks  of  the  authors  are  gratefully  given  to  all  those 
who  have  generously  assisted  them  in  securing  descriptions 
and  illustrations  of  chemical  processes  as  they  are  actually 


vi  PREFACE   TO  REVISED  EDITION 

carried  on.  Mr.  Allen  B.  Doggett  has  rendered  great  assist- 
ance in  photographic  work.  We  are  especially  indebted  to 
Professor  Charles  F.  Chandler,  of  Columbia  University  ;  to 
Mr.  C.  D.  McArthur ;  to  Professor  L.  H.  Merrill,  of  the  Uni- 
versity of  Maine;  to  Professor  Herbert  E.  Moody,  of  the 
College  of  the  City  of  New  York ;  to  Professor  Harmon  N. 
Morse,  of  Johns  Hopkins  University  ;  to  the  American  Smelt- 
ing and  Refining  Company,  L.  M.  Booth  Company,  Brooklyn 
Union  Gas  Company,  the  Carborundum  Company,  the  Crucible 
Steel  Company  of  America,  National  Lead  Company,  Standard 
Oil  Company,  United  Sulphur  Company,  and  to  the  /Scientific 
American,  for  assistance  which  they  have  rendered. 

NEW  YORK,  June,  1915. 


/' 

*Vl\ 


CONTENTS 

CHAPTER  PAGE 

I.  Introduction  ........         1 

ffl.  Gases  and  their  Measurement        .         .        .         .10 

III.  Oxygen 22 

IV.  Hydrogen 33 

V.  Composition  of  Water  and  Combining  Weights       .       43 

rl.  Water  and  Solution       .        .         .        .        .         .50 

rll.     Atoms  and  Molecules 64 

VIII.     Chlorine 71 

IX.     Hydrochloric  Acid 80 

X.     Molecular  Composition 89 

^JCI.  Atomic  and  Molecular  Weights      ....       95 

^All.  Chemical  Formulas  and  Names     .        .        .        .102 

-XIII.  Chemical  Equations      .        .         .         .        .         .116 

~^CIV.     Chemical  Calculations 125 

XV.     Sodium  and  Potassium 135 

XVI.     Solution         .         .         .         .' 143 

XVII.     Chemical  Equilibrium 160 

XVIII.  Sodium  and  Potassium  Compounds        .         .        .171 

XIX.     Sulphur  and  Sulphides 189 

XX.     Oxides  and  Acids  of  Sulphur 204 

XXI.  Nitrogen  and  the  Atmosphere         .        .        .         .221 

XXII.     Nitrogen  Compounds 233 

vii 


viii 


CONTENTS 


CHAPTBR 

XXIII. 

Elements  of  the  Nitrogen  Group 

PAGB 

257 

XXIV. 

The  Halogens                   ..... 

268 

XXV. 

Carbon    ........ 

288 

XXVI. 

Oxides  of  Carbon     

305 

XXVII. 

Silicon  and  Boron    

319 

XXVIII. 

Calcium  and  its  Compounds     .... 

329 

XXIX. 

Magnesium,  Zinc,  and  Mercury 

343 

XXX. 

Iron  and  Steel          ....... 

358 

XXXI. 

Iron  and  its  Compounds    

375 

XXXII. 

Copper  and  its  Compounds        .... 

384 

XXXIII. 

Silver,  Gold,  and  Platinum        .... 

396 

XXXIV. 

Aluminum  and  its  Compounds  . 

412 

XXXV. 

Tin  and  Lead  ....... 

428 

XXXVI. 

Manganese,  Chromium,  Cobalt,  and  Nickel 

439 

XXXVII. 

The  Periodic  Law   

450 

XXXVIII. 

Industrial  Carbon  Compounds  .... 

459 

XXXIX. 

Classes  of  Carbon  Compounds 

474 

XL. 

Radium  and  Radioactivity       .... 

494 

APPENDIX: 

I. 

Physical  Constants  of  the  Important  Elements  . 

506 

II. 

Table  of  Solubilities         

508 

III. 

General  Rules  for  Solubility      .         ... 

509 

IV. 

Volatility  of   Compounds  that  may  result  from 

Double  Decompositions        .... 

509 

V. 

Approximate  Weight  of  One  Liter  of  Common 

Gases  under  Standard  Conditions  . 

509 

VI. 

Pressure  of  Water  Vapor,  or  Aqueous  Tension  . 

510 

INDEX 

i                 ........ 

511 

PORTRAITS  OF  DISTINGUISHED  CHEMISTS 

FACING   PAGK 

Antoine  Laurent  Lavoisier 2 

Joseph  Priestley 2 

Robert  Wilhelm  Bunsen 26 

John  Dalton 44 

Theodore  W.  Richards 96 

Edward  Morley  .........  96 

Johann  Jacob  Berzelius 108 

Sir  Humphry  Davy t  .  136 

Michael  Faraday         .        . 148 

Svante  August  Arrhenius 152 

Jacobus  Henricus  van't  Hoff       .        .        .        .         .        .152 

Hamilton  Young  Castner     .         .         .         .'        .         .         .172 

Ernest  Solvay 172 

Herman  Frasch 190 

Sir  William  Ramsay 228 

Edward  Goodrich  Acheson  .......  294 

Charles  Martin  Hall    .         .        .       ..'        .        .        .        .412 

Dimitri  Ivanovitch  Mendelejeff 450 

Robert  Kennedy  Duncan 464 

Marie  Slodowska  Curie                                 .                 .        .  494 


FIRST   PRINCIPLES   OF  CHEMISTRY 


CHAPTER   I 
INTRODUCTION 

1.  Physical  Change.  —  When  we  notice  the  things  about 
us,  we  see  that  they  undergo  changes:  a  piece  of  wood 
bends  under  a  weight,  or  warps  when  wet  ;  a  rod  lengthens 
when  heated;    a  piece  of  iron  placed  near  a  magnet  at- 
tracts another  piece  of  iron.     If  we  remove  the  weight 
from  the  stick,  it  straightens;  the  iron  removed  from  the 
magnet  loses  its  power  of  attraction.     In  such  changes, 
although  the  object  may  be  considerably  altered,  we  still 
recognize  the  pieces  of  the  stick  as  wood,  as  we  do  the 
fragments   of   &    (broken   tumbler   as   glass  ;    that  is,  the 
material  has  not  lost  or  changejLthose  peculiar  properties 
or   the   characteristics   by  which    we   identify  TE     Such 
changes  are  called  physical  changes  ;   they  result  usually 
in  a  change  of  such  properties  as  sjze,  ghape^pr  color. 

2.  Chemical  Change.  —  Another  kind  of  change  is  seen  in 
the  burning  of  wood.     Iron  in  rusting  falls  to  a  red  powder  ; 
mortar  and  cement  change  from  a  plastic  to  a  stonelike 
condition;     fruits   and    vegetables   decay;     meat   spoils; 
milk  sours;  fruit  juices  ferment.     In  all  these  changes  the 

have  apparently  lo^tthe^entitv,  and   sub- 


^ 

stances  with  new  characteristics  are  forip^tU  >    We  dp  not 
find  any  resemblance  between  iron  aticT  fust*'6? 
wood  and  what  remains  after  it  is^burtfecj.   ;  -Tt^ 
the  wood  have  apparently  disappeared  or  change^  a 

1 


2  INTRODUCTION 

have  new  substances  in  their  places.  Such  alterations 
are  called  chemical  changes.  Chemistry  is  the  name  given 
to  the  science  which  has  grown  out  of  the  study  of  chem- 
ical changes  and  the  effort  to  control  or  modify  them. 

The  most  striking  chemical  change  that  goes  on  about 
us  is  that  which  occurs  when  a  substance  burns.  If  the 
burning  substance  is  coal  or  wood,  it  seems  to  disap- 
pear except  for  a  small  quantity  of  ashes.  In  studying 
this  change,  several  questions  suggest  themselves.  What 
has  happened  to  produce  the  heat  that  is  given  off? 
What  has  become  of  the  great  mass  of  substance  that  has 
apparently  disappeared  ?  Why  does  the  substance  burn 
more  brightly  when  air  is  blown  on  it  ?  Why  does  it 
stop  burning  when  the  air  is  shut  off,  as  in  smothering  a 
flame  ?  If  we  find  answers  to  these  questions,  we  shall 
have  explained  the  phenomena  of  burning. 

Early  investigators  did  not  discover  the  true  nature  of 
this  process.  They  adopted  a  wrong  explanation,  and,  as 
a  result,  the  science  of  chemistry  did  not  advance.  A  true 
explanation  was  stated  only  a  little  more  than  a  hundred 
years  ago.  Since  that  time  chemistry  has  progressed  at 
an  astonishing  rate.  The  true  explanation  of  burning  was 
found  by  studying  the  change  that  many  metals  undergo 
when  heated  in  air. 

3.  Heating  Metals  in  Air.  —  A  few  metals  —  for  example, 
magnesium  —  burn  when  heated  in  the  air.  Most  metals 
undergo  a  similar,  but  much  slower,  change,  without  the 
production  of  light.  If  a  piece  of  bright  copper  is  heated, 
it  assumes  a  black  color ;  on  bending  or  scraping  it  gently, 
&  black  powde?  ^epsjrates  from  it.  If  the  metal  is  heated 
anetilep  lay  el'  of  tthe  black  substance  forms.  By  re- 
rsufficient  number  of  times,  the  piece 
"be  'e'ntirely  changed  into  the  black  powder. 


Antoine  Laurent  Lavoisier 

(1743-1794)  was  a  French  in- 
vestigator and  scientific  inter- 
preter. When  twenty-five,  he 
was  chosen  adjunct  member 
of  the  French  Academy,  and 
became  one  of  the  leading 
scientists  of  his  time. 

Lavoisier  studied  combus- 
tion and  showed  by  quantitative 
experiments  that  the  weight  of 
the  product  exceeds  the  weight 
of  the  fuel.  He  explained  the 
composition  of  air  and  of  water 
and  advanced  the  doctrine  of 
indestructibility  of  matter. 


Joseph  Priestley  (1733-1804) 
was  an  English  writer  on  re- 
ligion, politics,  and  science. 
He  was  a  brilliant  investigator 
and  experimenter.  His  experi- 
ments suggested  to  him  that 
plants  and  animals  produce 
opposite  changes  in  the  air. 

Priestley  discovered  several 
gases,  notably  oxygen.  This 
he  prepared  by  heating  mer- 
cury oxide. 

The  latter  years  of  Priest- 
ley's life  were  passed  in  Penn- 
sylvania. 


\ 


-  P*  i*      - 

LAVOISIER'S  EXPERIMENT  3 

Since  the  black  powder  in  no  way  resembles  the  copper 
from  which  it  was  prepared,  a  chemical  change  has  taken 
place.  Iron  heated  in  a  similar  manner  gives  a  somewhat 
similar  result.  Lead  after  melting  gives  a  yellowish 
powder ;  zinc,  if  in  the  form  of  a  powder,  will  take  fire 
and  yield  a  white  powder.  Metals,  in  general,  when  thus 
heated  produce  powdered  substances  which  bear  little  or 
no  resemblance  to  the  original  metal.  In  some  cases  the 
change  is  very  slow  and  often  difficult  to  bring  about,  un- 
less the  metal  is  in  small  pieces  or  powdered  and  the  heat- 
ing carefully  regulated.  Gold  and  platinum  show  no 
change  on  heating  in  the  air. 

Several  things  may  be  thought  of  as  explanations  of  the 
change  which  the  metals  first  described  undergo.  It  may 
be  that  by  the  effect  of  the  heat,  without  the  aid  of  any 
substance,  the  metal  is  transformed  into  a  new  kind  of 
matter;  possibly  the  metal  in  being  heated  has  lost  some 
of  its  substance,  which  has  passed  off  as  gas ;  possibly  the 
metal  has  absorbed  something  from  the  air. 

As  an  aid  in  testing  these  possible  explanations,  it  will 
be  advisable  to  weigh  the  metal  before  and  after  it  is 
heated.  When  this  is  done,  it  will  be  found  that  the  pow- 
jfer  always  weighs  mor^Jhan  the  metal  from  which  it  was 
formed.  „  This  seems  to  indicate  that  during  the  heating 
the  metal  adds  to  itself  more  substance,  and  that  this  sub- 
stance is  taken  from  the  air.  To  further  test  this  conclu- 
sion, a  piece  of  metal  can  be  sealed  in  a  glass  tube  from 
which  the  air  has  been  exhausted ;  heated  under  these  con- 
ditions, the  metal  is  not  changed. 

4.  Lavoisier's  Experiment.  —  Another  conclusive  experi- 
ment showing  the  change  of  metals  on  being  heated  in  the 
air  is  one  that  was  performed  by  Lavoisier,  the  French 
chemist,  to  whom  is  given  the  credit  of  discovering  the 


4  INTRODUCTION 

nature  of  this  kind  of  chemical  change.  He  put  some  tin 
in  a  good-sized  glass  flask  and  sealed  it  so  that  the  air 
could  neither  enter  nor  leave  it.  He  then  heated  the  flask 
carefully  for  several  days.  At  the  end  of  this  time,  he 
noticed  that  a  certain  amount  of  white  powder  had  been 
formed.  He  next  ascertained  that  the  flask  with  its  con- 
tents had  not  changed  in  weight.  He  then  opened  the 
neck  of  the  flask  and  noticed  that  air  rushed  in.  On 
again  weighing  the  flask  and  its  contents,  he  found  that 
there  was  an  increase  in  weight,  and  that  this  increase 
was  equal  to  the  increase  which  the  tin  had  undergone  on 
being  converted  into  the  white  powder.  He  explained 
these  facts  as  follows  :  the  tin  on  being  heated  combined 
with  some  of  the  air  in  the  flask,  producing  the  white 
powder.  The  flask  as  a  whole  did  not  increase  in  weight 
because  no  air  entered  the  flask  to  take  the  place  of  that 
which  had  combined  with  the  tin.  When  the  flask  was 
opened,  the  air  entered,  causing  the  increase  in  weight. 
Since  experience  has  shown  that 


createjjnor  destroyed,  it  appears  probable  that  the  powdered 
substances  are  more  complex  than  the  metals  from  which 
they  are  formed  ;  that  is,  they  contain  the  metal  plus 
something  which  has  been  taken  from  the  air.  Lavoisier 
undertook  to  find  out  the  nature  of  the  substance  which 
was  taken  from  the  air. 

5.  Heating  Mercury  in  the  Air.  —  Mercury,  heated  in  the 
air,  underwent  a  much  less  rapid  change  than  the  metals 
of  which  we  have  been  speaking.  Kept  at  a  temperature 
a  little  below  its  boiling  point  for  several  days  a  small 
quantity  of  red  powder  was  gradually  formed  (Fig.  1). 
A  quantity  of  this  powder  was  heated  in  a  glass  tube  to 
a  temperature  above  the  boiling  point  of  mercury,  and  a 

colorless  gas  was  given  off. 
9  —          ° 


HEATING  MERCURY  IN  THE  AIR  5 

A  glowing  splinter  was  inserted  into  the  tube.  It 
burst  into  flame  and  burned  brilliantly.  The  gas  could 
not  have  been  ordinary  air,  for  a  splinter  does  not  behave 
so  in  air.  A  quantity  of  the  gas  was  collected  and  was 
shown  to  be  very  different  from  ordinary  air  by  the  fact 
that  substances  burned  in  it  with  extraordinary  vigor. 

On  examining  the  tube  it  was  found  that  a  part  or  all 


FIG.  1.  —  LAVOISIER'S  APPARATUS  FOR  HEATING  MERCURY. 

of  the  red  powder  had  disappeared  and  that  drops  of  mer- 
cury had  collected  on  the  sides  of  the  tube.  It  appears 
from  this  experiment  that  the  red  powder  had  decomposed 
into  mercury  and  a  gas  which  readily  supports  combustion. 
Lavoisier  named  this  gas  oxygen. 

Since  the  red  powder  was  made  by  heating  mercury  in 
the  air,  and  was  not  formed  unless  air  was  present,  the 
oxygen  must  have  come  from  the  air.  Hence  air  must  con- 
tain oxygen.  That  air  is  not  all  oxygen  is  shown  by  the 
fact  that  only  about  one  fifth,  and  not  all,  of  the  air  was 
absorbed  in  Lavoisier's  experiments;  and  also  by  the  fact 
that  substances  do  not  burn  as  readily  in  air  as  in  oxygen. 


6  INTRODUCTION 

The  powders  obtained  by  burning  tin  or  copper, or  iron 
weigh  more  than  the  original  piece  of  metal,  because  the 
metal  has  .combined  with,  a  noticeable  weight  of  oxygen 
from  the  air.  In  these  cases,  it  is  not  practical  to  separate 
the  metal  from  the  oxygen  by  heat  alone. 

6.  Burning.  —  The  burning  of  wood  or  other  substances 
is  a  process  that  closely  resembles  the  change  of  a  metal 
into  a  compound  of  the  metal  and  oxygen.     In  the  case  of 
ordinary  combustible  materials,  the  products  are  chiefly 
gases  which  pass  off  unseen.     By  the  use  of  suitable  ap- 
paratus, the  products  formed  in  the  burning  of  a  candle 
can  be  collected,  and  it    is   found  that  their  weight   is 
greater^  than  the  weight  of  the  candle  burned.     As  in  the 
case  of  the  metals,  this  increase  in  weight  is  due  to  the 
oxygen  taken  up  from  the  air.     If  air  is  excluded,  the  burn- 
ing substance  is  extinguished,  because  it  can  no  longer 
combine  with  oxygen. 

7.  Compounds  and  Elements.  —  We  have  shown  that  the 
red  substance  contains  oxygen  and  mercury.  -<  The  sub- 
stance formed  on  heating  copper  in  the  air  contains  oxygen 
and  copper..     As  these  substances  formed  are  composed  of 
more  than  one  kind  of  material,  they  are  called  compounds. 
A.  compound  is  a  substance  that  can  be  separated  into  two 
or  more  substances.     No  one  has  changed  copper  or  mer- 
cury into  anything  else,  without  adding  something.     So  far 
as  we  know,  gold,  iron,  oxygem-ajid  about,  eighty  other 
things   are   not   composed  of   anything  else.      They  are 
simple  substances,  or,  as  we  say,  elements.     An  element  is  a 
substance  that  has  not  been  separated  into  other  substances 
by  man.     A  list  of  elements  is  given  in  Table  I,  Appendix. 


8.   Solids,    Liquids,   and  Gases. — We    have    spoken 
metals,  powders,  air,  and  oxygen  as  things  that  may 


of 
be 


IDENTIFYING  SUBSTANCES  1 

weighed.  They  are  forms  of  matter.  Matter  is  generally 
defined  as  any  thing  that  ocnnpips  spanft.  The  different 
kinds  of  matter  are  called  substances.  Substances  differ 
in  the  way  they  fill  space,  and  it  is  this  difference  that 
determines  their  physical  state.  The  three  physical  states 
of  matter  are  the  solid,  the  liquid,  and  the  gaseous. 

A  solid  has  a  definite  shape  or  form,  and  a  definite 
volume.  A  liquid  has  no  definite  form,  but  has  a  definite 
volume.  It  can  fill  a  vessel  only  to  the  extent  of  its  volume 
and  takes  the  shape  of  the  containing  vessel  so  far  as  it 
fills  it.  G-ases  have  neither  a  definite  form  nor  a  definite 
volume.  They  tend  to  distribute  themselves  in  all  direc- 
tions and  fill  completely  any  vessel  into  which  they  are 
brought.  Their  only  boundaries  are  the  containing  walls. 

9.  Identifying  Substances.  —  The  different  kinds  of  mat- 
ter are  identified  by  their  properties  or  peculiarities.  The 
more  important  of  these  are  given  in  the  table  below. 

Physical  properties  used  in  identifying  substances : 


SOLID  STATE 

Density  or 

relative  weight; 
melting  poin£; 

luster,  hardness; 
color,  taste,  or 

smell; 
solubility. 


LIQUID  STATE 

Density  or 

relative  weight ; 
freezing  point; 
boiling  point; 

color,  taste,  or 

smell; 
solubility. 


GASEOUS  STATE 

Density  or 

relative  weight; 

condensing  point; 

color,  taste,  or 

smell ; 
solubility. 


Chemical  properties  used  in  identifying  substances: 
Reactions  with  air  or  oxygen; 
Reactions  with  water; 
Reactions  with  acids  or  bases; 
Actions  Deculiar  to  the  substance  or  its  constituents. 


8  INTRODUCTION 

SUMMARY 

Chemical  changes  involve  changes  in  the  identity  of  the  material. 
The  composition  of  the  substance  is  usually  altered,  and  energy 
changes  are  also  involved. 

A  compound  is  a  substance  that  can  be  separated  into  two  or 
more  substances.  An  element  is  a  substance  which  has  not  been 
separated  into  other  substances  by  man. 

So  far  as  known,  matter  cannot  be  created  nor  destroyed.  (This 
statement  is  known  as  the  Law  of  the  Conservation  of  Matter.) 

When  a  substance  burns  in  air,  it  combines  with  oxygen,  form- 
ing a  new  compound. 

Lavoisier  obtained  oxygen  from  air  by  heating  mercury  in  it 
and  then  decomposing  the  material  produced. 

EXERCISES 

1.  Air  and  water  were  formerly  called  elements.     Why  are 
they  not  now  ? 

2.  How  could  you  prove  that  air  contains  oxygen  ? 

3.  What  kind  of  change  is  involved  in  the  withering  of  a 
leaf  ?     Making  cloth  from  wool  ?     Baking   bread  ?     Burning 
coal  ?    Extinguishing  the  fire  ? 

4.  Why  is  a  burning  candle  extinguished  by  blowing  ? 

5.  Describe  experiments  that  you  performed  in  the  labora- 
tory which  illustrate  the  difference  between  physical  and  chemi- 
cal change. 

6.  Distinguish  between  the  terms  element  and  compound. 

7.  Give  three  examples  of  chemical  change,  each  producing 
a  different  form  of  energy. 

•    *A^iA^.«  -       lV-,-w     ViA/vti/VA^, 

8.  When  2  grams  of  a  certain  substance  were  heated,  all 
the  oxygen  which  the  substance  contained  was  given  off,  and  a 
residue  weighing  1.07  grams  was  left.    Calculate  the  percentage 
of  oxygen  in  the  substance. 


EXERCISES  9 

9.   Why  is  the  crushing  of  glass  a  physical  change  ? 

10.  Name  three  chemical  changes  which  occur  in  the  kitchen ; 
three  physical  changes. 

11.  What  kind  of  changes  are  involved:    in  the  digestion 
of  food  ?     The  tanning  of  hides  ?     The  raising  of  your  arm  ? 
The  ripening  of  fruits  ?     Paring  of  potatoes  ? 

12.  How  would  you  show  that  lead,  when  heated  in  the  air, 
combines  with  something  to  form  a  yellowish  powder  ? 

13.  What   is   the   difficulty   in  proving  that  the  products 
formed  by  burning  a  candle  weigh  more  than  the  candle  ? 

14.  What  always  happens  when  a  substance  burns  in  air  ? 

15.  How  did  the  failure  of  the  earlier  investigators  to  use  a 
balance  prevent  them  from  finding  the  true  explanation  of 
burning  ? 


/D 

•/  ' 

-^ — 

,r 


CHAPTER  II 
GASES  AND  THEIR  MEASUREMENT1 

10.  Gas  Pressure.  —  The  peculiar  properties  of  gases  are 
due  to  the  fact  that  the  particles  composing  them  are 

at  considerable  dis- 
tances from  each 
other  and  are  in 
rapid  motion.  As 
these  particles  pelt 
against  the  walls  of 
the  containing  ves- 
sel^ they  exert  a 
pressure  on  the 
walls.  If  a  gas  is 
compressed  into  a 
smaller  space,  more 
particles  will  strike 
a  square  inch  in  a 
given  time,  and  so 
the  pressure  meas- 
ured in  pounds  per . 
square  inch  is  in- 
creased. The  in- 
creasing pressure  of  the  air  in  a  bicycle  pump,  as  the 
piston  is  forced  down,  illustrates  this.  If  a  gas  is 
heated  without  being  allowed  to  expand,  its  pressure  on 

1  If  the  instructor  prefers,  this  chapter  may  be  introduced  later  or 
used  for  reference  in  connection  with  the  laboratory  work,  without  inter- 
fering with  the  continuity  of  the  course. 

10 


FIG.  2.  —  STEAM  GAUGES. 


I     ' 


-750 


EFFECT  OF  TEMPERATURE  AND  PRESSURE     11 

the  walls  of  the  vessel  containing  it  will  be.  increased,  be- 
cause the  heat  increases  the  speed  of  the  particles. 

The  air  which  surrounds  us  is  compressed  by  the  weight 
of  the  atmosphere  above  it.  The  pressure  due  to  the 
weight  of  atmosphere  is  about  15  pounds  per  square  inch 
at  sea  level  and  is  less  at  higher  alti- 
tudes. It  is  not,  however,  a  constant 
quantity,  but  varies  with  weather  con- 
ditions. While  the  pressure  of  con- 
fined gases,  like  steam  or  compressed 
air,  is  measured  by  a  pressure  gauge 
(Fig.  2),  atmospheric  pressare^  IB 
measured  by  the  height  of  the  column 
of  mercury  that  it  supports  in  a 
barometer  (Fig.  3). 

The  barometer  consists  of  a  tube 
^which  has  been  entirely  filled  with 
mercury  and  then  inverted  into  a 
reservoir  of  the  same  liquid.  A  pre&- 
sure  of  14.7  pounds  per  square  inch 
is  equal  to  the  weight  of  a  column  of 
mercury  1  in.  square,  and  30  in.  or 
760  mm.  high.  As  the  gases  whose 
volume  we  measure  in  the  laboratory 
are  usually  subject  to  atmospheric 
pressure,  gas  pressures  in  chemical 
work  are  usually  expressed  in  milli- 
meters of  mercury  instead  of  pounds  vper  square  inch. 


FIG.  3.  —  BAROMETER. 

a,  Section  ;  b,  Ex- 
ternal view. " 


11.  Effect  of  Temperature  and  Pressure  Changes  on  Volumes 
of  Gases.  —  The  measurement  of  the  volume  of  gases  usually 
involves  a  correction  of  the  gas  volume.  This  is  necessary 
because  the  volume  of  a  given  quantity  of  gas  is  consider- 
ably affected  by  even  slight  changes  in  temperature  and 


12  GASES  AND   THEIR   MEASUREMENT 

pressure.  If  the  room  gets  warmer,  the  volume  will  be 
larger;  if  it  gets  colder,  the  volume  will  be  less.  Changes 
in  atmospheric  pressure  will  also  cause  the  volume  to  vary. 
An  increased  pressure  will  mean  a  diminished  volume,  and 
a  decreased  pressure  an  increased  volume. 

The  measurement  of  gases  in  experiments  like  the 
analysis  of  air  will  be  of  little  value  for  accurate  work 
unless  account  is  taken  of  the  temperature  and  pressure 
changes.  For  this  reason  it  becomes  necessary  to  know 
to  what  extent  these  affect  the  volumes.  This  is  not  a 
difficult  matter,  for  it  is  found  that  all  gases  contract  or 
expand_tQ,almost  exactly  the  same  degree  when  they  are 
subjected  to  the  same  changes.  This  regularity  is  some- 
what surprising.  A  similar  thing  is  not  at  all  true  for  solids 
or  liquids.  Any  observed  regularity  of  this  sort  is  called 
a  law. 

12.  Charles'  Law.  —  It  is  found  that  if  a  certain  quantity 
of  any  gas  is  made  to  have  a  temperature  of  0°  C.,  and 
then  is  warmed  one  degree,  the  gas  expands  gy^  of  its 
volume.  Warmed  to  10°,  it  expands  fflg  of  its  volume. 
Heated  to  273°,  its  volume  will  be  doubled.  On  cooling 
the  gas,  we  find  that  it  contracts  gy^  of  its  volume  at  0°  O 
for  each  degree.  At  —  273°  C.  the  volume  of  the  gas  would 
be  zero,  if  contraction  continued  at  the  same  rate.  As  a 
matter  of  fact,  all  known  gases  become  liquids  before  this 
temperature  is  reached. 

This  point,  —  273°  C.,  has  been  selected  as  the  zero  of 
another  temperature  scale  known  as  absolute  temperature 
(Fig.  4).  Since  the  size  of  the  absolute  degree  is  the 
same  as  the  Centigrade  degree,  and  since  the  absolute 
zero  is  273  degrees  below  the  Centigrade  zero,  a  Centi- 
grade temperature  is  changed  to  an  absolute  tempera- 
ture by  adding  it,  algebraically,  to  273.  Thus,  24°  C. 


USE   OF  CHARLES'  LAW 


13 


becomes   297°  abs.  (273+24);    -12°  C.    becomes  261G 
abs.   (273-12). 

The  general  statement  of  the  relation  between  the  vol- 
ume of  a  gas  and  its  temper-  CENTIGRADE  ABSOLUTE 
ature  is  known  as  Charles'  ioov- 
Law.  Charles'  Law  may  be 
stated  thus : 


The  pressure  remaining 
the  same,  the  volume  of  a 
gas  varies  directly  as  the  ab- 
solute temperature. 

13.  Use  of  Charles'  Law  in 
correcting  Gas  Volumes.  — 
By  using  this  law  we  can 
calculate  what  will  be  the 
volume  of  a  gas  at  a  tem- 
perature differing  from  that 
under  which  it  is  measured. 
For  example,  a  quantity  of 
air  measures  25.6  c.c.  at  a 
temperature  of  21°.  £-  Find 
its  volume  at  0°. 

21°  C.  =  294°  abs. 
0°  C.  =  273°, 


oc- 


^[-  -Room  Temperature 
Freezing_Pomt_ 


of  Water 


of  Water 


•273° 


20.5° 


—252  5  -  • 

Hydrogen 

-2t3  °  -L  -  -Absolute  Zero-  -  -L 
FIG.  4.  —  CENTIGRADE  AND  ABSOLUTE 
TEMPERATURE  SCALES. 


If  the  temperature  of  the 
gas   were  actually  changed 
from  294°  to  273°,  it  would  be  cooled,  and  would  therefore 
contract.     The  volume  at  273°  will  be  less  than  the  orig- 
inal volume.     The  fraction  of  the  original  volume  will, 
therefore,  be  |^J  of  its  former  volume.     Hence: 
a;  =25.6  c.c.  x  f  £f 
=  23)7  c.c. 


14  GASES  AND   THEIR  MEASUREMENT 

14.  Correction  for   Temperature.  —  The   temperature   of 
0°  C.  (  =  273°  abs.)  is  chosen  as  the  standard  temperature 
for  the  measurement  of  gas  volumes.     The  operation  of 
finding  the  volume  at  the  standard  temperature  is  called 
correcting  the  volume  for  temperature.     Sometimes   it   is 
necessary  to  find  the  volume  at  a  temperature  other  than 
the  standard  temperature.     The  operation  is  a  similar  one. 

Example:  A  quantity  of  gas  has  a  volume  of  75  c.c.  at 
a  temperature  of  24°.  What  will  be  its  volume  at  100°  ? 

Since  the  temperature  is  increased,  the  volume  will  also 
be  increased.  The  fraction  by  which  the  original  volume 
is  to  be  multiplied  is  therefore  greater  than  one. 

x  =  75  c.c.  x  HI 
=  94.2  c.c. 

15.  Boyle's  Law.  —  Experiment  shows  that  if  the  pressure 
on  any  gas  is  doubled  and  the  temperature  kept  constant, 
the  resulting  volume  will  be  one  half  the  original  volume. 
Under  a  pressure  three  times  as  great,  the  volume  is  one 
third.    If  the  pressure  is  made  one  third  the  original  pres- 
sure, the  volume  will  become  three  times  the  original  vol- 
ume.    In  general,  the  greater  the  pressure,  the  less  the 
volume   in  a  proportional   degree.     This  generalization, 
known  as  Boyle's  Law,  is  usually  stated  thus  : 

The  temperature  remaining  the  same,  the  volume  of  a  gas 
varies  inversely  as  the  pressure  exerted  upon  it. 

16.  Use  of  Boyle's  Law  in  the  Correction  of  Gas  Volumes. 

—  Boyle's  Law,  like  Charles'  Law,  enables  us  to  calculate 
the  volume  of  a  given  quantity  of  gas  under  new  condi- 
tions. For  example,  a  quantity  of  gas  has  a  volume  of 
120  c.c.,  the  barometer  standing  at  740  mm.  What  will 
be  the  volume  when  the  atmospheric  pressure  has  increased 
until  the  barometer  stands  at  760  mm.  ? 


CORRECTION  FOR  PRESSURE  15 

The  numbers  740  mm.  and  760  mm.  are  measures  of 
the  two  pressures.  The  new  volume  will  be  found  by 
multiplying  the  original  volume  by  the  ratio  of  these  two 
numbers.  It  is  apparent  that  the  gas  will  be  subjected  to 
a  greater  pressure  under  the  new  condition.  According 
to  the  law,  its  volume  will  be  less.  The  fraction  will  there- 
fore have  the  less  number  as  the  numerator.  Hence : 
J  h 


=  116.8  c.c. 

17.  Correction  for  Pressure.  —  The  standard  pressure  for 
measuring  gases  is  the  pressure  that  the  atmosphere  exerts 
when  the  barometer  stands  at  jT60  mm.     This  is  the  aver- 
age height  of  the  barometer  at  sea  level.     The  operation 
of  finding  the  volume  of  a  gas  at  this  pressure  is  called 
correcting  the  gas  for  pressure.     The  volume  of  a  gas  at 
any  pressure  whatever  is  found  in  a  similar  manner. 

Example  :  A  quantity  of  air  measures  82.2  c.c.  at  520  mm. 
pressure.  What  will  be  the  volume  at  800_mm.,  the  tem- 
perature remaining  constant  ? 

It  is  evident  that  the  resulting  volume  will  be  less  than 
the  original,  since  the  pressure  under  the  new  condition  is 
increased.  Hence  the  ratio  by  which  the  original  volume 
is  multiplied  must  be  less  than  one. 

#  =  82.2  xfU 
=  53.4  c.c. 

18.  Simultaneous  Correction  for  Temperature  and  Pressure.  — 
These  two  corrections  can  be  carried  out  in  one  arithmet- 
ical operation,  for  the  temperature  effect  and  the  pressure 
effect  are  entirely  independent  of  each  other.     For  exam- 
ple, a  quantity  of  gas  measures  206  c.c.  at  a  temperature 
of  22°  and  a  pressure  of   750  mm.     What  will  be  the 


16 


GASES  AND   THEIR   MEASUREMENT 


volume  of  the  gas  under  standard  conditions  of  tempera- 
ture and  pressure  ? 


Temperature       Pressure 
correction        correction 


x  =  206      x 
=  188.1  c.c. 


^13        x        750 
195        X        7  6  ft 


FIG.  5.        FIG.  6.        FIG.  7. 


19.  Correction  for  Difference  in 
Level.  —  Gases  are  usually  meas- 
ured in  bottles  or  tubes  that 
stand  over  liquids.  The  liquid, 
as  a  rule,  is  either  water  or  mer- 
cury. In  order  that  the  pressure 
of  the  gas  inclosed  under  these 
conditions  shall  be  equal  to  the 
atmospheric  pressure,  the  levels 
of  the  liquid 


outside  and  inside  the  tube,  must  be  the 
same  (Fig.  5).  This  condition  is  usu- 
ally realized  by  adjusting  the  appara- 
tus. Sometimes  this  is  impossible, 
and  then  it  is  necessary  to  correct  for 
the  difference  in  level.  This  is  done 
by  adding  to  or  subtracting  from  the 
height  of  the  barometer  a  suitable 
number.  When  the  inside  level  is 
the  higher,  the  pressure  on  the  inclosed 
gas  is  less  than  atmospheric  (Fig.  6), 
for  part  of  the  atmospheric  pressure  is 
used  in  supporting  the  column  of  liquid 
in  the  tube ;  when  the  inside  level  is 
the  lower,  the  pressure  is  greater  than 
atmospheric  (Fig.  7).  For  mercury, 
the  actual  difference  in  millimeters  is 
added  or  subtracted;  for  water,  one 


CORRECTION  FOR  PRESSURE  OF  WATER  VAPOR     17 

thirteenth  of  this  value  is  used,  since  water  is  about  one 
thirteenth  as  heavy  as  mercury. 

Example:  A  volume  of  gas  is  inclosed  in  a  tube  over 
mercury  (Fig.  8).  The  volume  of  gas  measures  68.3  c.c., 
and  the  level  of  the  mercury  inside  the  tube  is  114  mm. 
above  the  level  in  the  dish.  The  thermometer  reads  20°  C. 
and  the  barometer  766  mm.  Find  the  volume  of  the  gas 
at  standard  conditions. 

The  corrected  pressure  is  found  by  subtracting  114  mm. 
from  766  mm., 

766-114  =  652  mm. 

f  '  "     ^ 
The  gas  volume  will  be  corrected  to  standard  conditions 

as  follows : 

*  =  68,3  x  f|f  xfft 
=  54.6  c.c. 

-fl   fiv^.    , 

20.  Correction  for  Pressure  of  Water  Vapor.  —  When  a  gas 
is  confined  over  water,  some  of  the  water  evaporates  and 
mixes  with  the  gas.  In  such  a  case  the  pressure  of  the  gas- 
eous mixture  consists  of  two  parts,  one  due  to  the  gas  itself 
and  the  other  due  to  the  water  vapor.  The  total  pressure 
is  the  sum  of  these  two  pressures.  The  pressure  due  to 
water  vapor,  therefore,  must  be  subtracted  from  the  ob- 
served barometric  pressure  in  order  to  determine  the  actual 
pressure  of  the  dry  gas..  The  pressure  due  to  water  vapor 
depends  only  on  temperature,  and  not  on  any  other  con- 
ditions of  the  experiment.  It_isjilways  the  same  for  the 
game  temperature,  provided  the  gas  is  saturated  with  water 
vapor.  Tables  of  these  values  for  different  temperatures 
have  been  prepared  as  the  result  of  careful  experiments. 
(See  page  21.) 

Corrections  for  difference  in  level  and  for  the  pressure 
of  the  water  vapor  (which  is  sometimes  called  aqueous 


18 


GASES  AND    THEIR  MEASUREMENT 


,  tension^)  are  both  pressure  corrections.  They  are  made  by 
adding  to  or  subtracting  from  the  observed  barometric 
pressure  suitable  numbers.  These  corrections  are  parts, 
then,  of  the  pressure  correction. 

Example:  24.6  c.c.  of  nitrogen  is  contained  in  a  tube 
over  water.  The  level  of  the  water  inside  the  tube  is 
27  mm.  above  the  outside  level.  The  barometer  stands 
at  762  mm.,  and  the  thermometer  at  23°.  What  is  the 
corrected  pressure  ?  On  consulting  a  table  we  find  that 
the  pressure  of  aqueous  vapor  at  23°  is  approximately  21 
mm.  The  corrected  pressure  is  therefore  : 

Difference      Aqueous 
in  level         tension 

762  fj     -     21     =     739  mm. 

/  % 

21.  The  following  example  will  illustrate  in  full  the  opera- 
tion of  correcting  gas  volumes  : 


79.3  c.c. 
764     mm. 

21°  C. 
+  41     mm. 
18     mm. 


Volume  of  air 

Pressure  uncorrected   .... 

Temperature 

Difference  in  water  level  (Fig.  6) 
Aqueous  tension  at  21°     . 

Corrected  pressure  .     1  Ml  3- 

Corrected  volume  of  air 

The  corrected  pressure  is 

Difference      Aqueous 
in  level         tension 

764     -ft  18     =     743mm. 

21°  C.  =  294°  abs. 

If  the  temperature  of  the  gas  were  changed  from  294° 
absolute  to  273°  absolute,  its  volume  would  become  less. 
Hence  the  ratio  for  the  temperature  correction  is  | 


PROBLEMS  19 

Changing  the  pressure  from  743  to  760  mm.  would  also 
tend  to  diminish  the  volume;  the  pressure  correction  ratio 
is,  therefore,  ||-|.  The  final  calculation  is,  then  : 


=  71.  9  c.c. 

PROBLEMS 

1.  A  quantity  of  hydrogen  measures  53  c.c.  at  a  temperature 
of  20°.     What  would  it  measure  at  28°  ?    . 

n 

2.  What  volume  would  60  c.c.  of  oxygen,  measured  at  17°, 
occupy  at  0°?  ^"V,  o 

3.  Find  the  volume  65  c.c.  of  air  would  occupy,  if  its  tem- 
perature were  changed  fromr  —  13°  to  23°. 

4.  105  c.c.  of  oxygen  at  "27°  were  cooled  to  17°.     Find  the 
"  :  new  volume. 

5.  What  volume  would  39  c.c.  of  air  occupy  when  its  pres- 
sure changes  from  768.  mm.  to  750  mm.  ? 

6-   3^  c.c.  of  gas  were  measured  at  744  mm.  pressure.     Find 
the  volume  at  760  mm. 

7.  80.2  c.c.  of  air  stand  in  a  tube,  mercury  levels  adjusted; 
the  barometer  stands  at  768  mm.    The  next  day  it  reads  755  mm. 
What  volume  would  the  air  then  have  ? 

/?*tAv  t*_^tt^L.  '         /lT~fb        '"^  *  *^  *"  " 

8.  151  c.c.  of  nitrogen  stand  in  a  tube  over  water,  with  the 
~7  inside  level  139  mm.  above  the  outside  level.     What  volume 

*  would  the  gas  have  if  the.  two  levels  were  the  same,  the  tem- 
perature being  unchanged?     The  barometer  stands  at  754  mm. 

9.  How  much  would  52.2  c.c.  of  air  measure  if  the  barometric 
I  pressure  changed  from  750  mm.  to  762  mm.  ?     If  the  tempera- 

ture also  changed  from  18°  to  25°c?    / 

10.  A  quantity  of  air  and  water  vapor,  standing  over  water 
in  a  gas-measuring  tube,  levels   adjusted,  has   a  volume   of 
31.8  c.c.     The  temperature  is  26°  ;  the  barometer  stands  at 
737.6  mm.     Correct  the  volume  of  air  to  standard  conditions. 


20 


GASES  AND   THEIR   MEASUREMENT 


11.  A  quantity  of  air  and  water  vapor  in  a  tube  over  water, 
levels  adjusted,  measures  43  c.c.  The  thermometer  stands  at 
24°,  the  barometer  at  770  mm.  Correct  to  standard  conditions. 

In   the   following   cases    correct   the   volume   to   standard 

conditions : 

* /j?     7o  J 


VOLUME 

CONDITIONS 

TEMPER- 
ATURE 

BAKOMETER 

12. 

152  c.c. 

Over  mercury  ; 
levels  the  same. 

27° 

755  mm.  /j> 

13. 

1.26  c.c. 

Over  water;                     ^ 
levels  the  same. 

I  20° 

748mm.    f%  1 

14. 

210  c.c. 

Over  water  ; 
inside  level  80  mm. 

22° 

764mm.  / 

above  outside  level. 

15. 

15.2  c.c. 

Over  mercury  ; 
inside  level  30  mm. 

,21° 

760  mm. 

above  outside  level. 

16. 

129  c.c. 

Over  water  ; 
levels  the  same. 

17° 

770  mm. 

17 


]/, 


17.   A  volume  of  gas  (dry)  measures  58.5  c.c.  at  a  tempera- 
ture of  183°  and  a  barometric  pressure  of  759  mm.     Find  the 
volume  of  the  gas  under  standard  conditions. 
&  &O^Lk&&i-  /ft  *Ufat>t£t&/l0L 

""  f    * "•'      A'  __#     'V  #       " 

faft  rc-  , -  V--/A  <  ^  '3*4 


/*</ 


P< 


, 
* 


V  &  K  3 


TABLE   OF  AQUEOUS   TENSION 


21 


PRESSURE  OF  WATER  VAPOR  OR  AQUEOUS  TENSION 
(in  millimeters  of  mercury) 


TEMPERATURE 

PRESSURE 

TEMPERATURE 

PRESSURE 

10.0°  a 

9.2  mm. 

20.0°  C. 

17.4  mm. 

10.5 

9^5 

20.5 

17.9 

11. 

9.8 

21. 

18.5 

11.5 

10.1 

21.5 

19.1 

12. 

10.5 

22. 

19.7 

12.5 

10.8 

22.5 

20.3 

13. 

11.2 

23. 

20.9 

13.5 

11.5 

23.5 

21.5 

14. 

11.9 

24. 

22.1 

14.5 

12.3 

24.5 

22.8 

15. 

12.7 

25. 

23.5 

15.5 

13.1 

25.5 

24.2 

16. 

13.5 

26. 

25.0 

16.5 

14.0 

26.5 

25.7 

17. 

14.4 

27. 

26.5 

17.5 

14.9 

27.5 

27.3 

18. 

15.4 

28. 

28.1 

18.5 

15.9 

28.5 

28.9 

19. 

16.4 

29. 

29.8 

19.5 

16.9 

29.5 

30.7 

30. 

31.6 

CHAPTER   III 
OXYGEN 

22.  Preparation.  —  In  1774,  Priestly  obtained  oxygen 
from  a  red  powder  prepared  by  heating  mercury  in  the  air. 
When  this  powder  is  heated  at  a  temperature  somewhat 


D 


FIG.  9.  —  PREPARATION  OF  OXYGEN. 

A,  Bunsen  burner  ;  B,  tube  containing  potassium  chlorate  and  manganese 
dioxide  ;   C,  pneumatic  trough  ;  D,  D>  bottles  for  collecting  the  gas. 

higher  than  that  at  which  it  was  prepared,  it  is  decom- 
posed into  a  gas  (oxygen)  and  metallic  mercury. 

When  pure  oxygen  is  desired  in  quantity,  it  is  some- 
times prepared  from  potassium  chlorate  (Fig.  9),  a  com- 
pound of  potassium,  chlorine,  and  oxygen;  this,  when 


PROPERTIES    OF  OXYGEN  23 

heated,  melts  and  gives  oxygen  gas  and  a  residue  of  potas- 
sium chloride.  In  the  laboratory  it  is  customary  to  mix  the 
potassium  chlorate  with  manganese  dioxide,  as  it  is  found 
that  the  decomposition  is  more  regular  and  takes  place  at 
a  lower  temperature.  A  material  which  thus  aids  chemi- 
cal action,  without  being  permanently  altered,  is  called  a' 
catalytic  agent.  To  free  the  oxygen  from  dust  and  other 
impurities,  it  may  be  allowed  to  bubble  through  water. 

Oxygen  is  prepared  from  water  on  a  commercial  scale 
by  passing  an  electric  current  through  it  (§  33). 

23.  Physical  Properties.  —  Pure  oxygen  is  a  gas  without 
color,  taste,  or  odor.     It  is  slightly  more  dense  than  air. 
It  dissolves  somewhat  in  water;  under  ordinary  conditions, 
100  volumes  of  water  dissolve  3  volumes  of  oxygen.     If 
ordinary  faucet  water  be  allowed  to  stand  in  a  glass,  or  if 
the  water  be  warmed,  bubbles  will  be  observed  clinging 
to  the  sides  of  the  glass  before  the  water  actually  boils. 
Such  bubbles  are  largely  oxygen,  which  was  dissolved  in 
the  water. 

If  cooled  sufficiently,  oxygen  condenses  to  a  pale  blue 
liquid,  and,  on  still  further  cooling,  solidifies. 

24.  Chemical  Properties.  —  The  most   noticeable  chemi- 
cal property  of  oxygen  is  its  tendency  to  combine  with  other 
elements.     At  ordinary  temperatures,  it  does  not  readily 
react  with  many  substances,  but  at  higher  temperatures 
its  action  is  rapid,  and  is  usually  accompanied  by  heat  and 
light.     Nearly  all  the  elements  combine  readily  with  oxy- 
gen to  form  compounds  known  as  oxides. 

25.  Combustion  is  a  chemical  action  by  which  heat  and 
light   are   evolved.     Lavoisier,  in  1786,  was  the  first  to 
explain  ordinary  burning  as  the  combining  of  a  substance 


24 


OXYGEN 


with  oxygen.  When  the  action  takes  place  rapidly,  the 
increase  in  temperature  is  appreciable,  and  light  may  re- 
sult (Fig.  10).  Thus,  when  a  piece  of  coal  burns,  the 
carbon  of  the  coal  combines  with  the  oxygen  of  the  air  to 
form  carbon  dioxide,  a  gas  which  passes  off  unseen;  at 
the  same  time  a  considerable  quantity  of  heat  is  evolved, 
and  the  neighboring  particles  .of  fuel  become  red-hot. 

As  the  air  is  only  about  one  fifth  oxygen,  substances  do 
not  burn  as  readily  in  it  as  in  pure  oxygen.     A  glowing 


FIG.  10.  —  PHOSPHORUS  BURNING  IN 
OXYGEN. 


FIG.  11.  —  RUSTING  OF 
IRON. 


splinter  plunged  into  oxygen  bursts  into  flame.  Charcoal 
glows  much  more  brilliantly  in  oxygen  than  in  air.  Sul- 
phur  burns  in  air  with  a  pale  blue  flame,  in  oxygen  vividly. 
Iron  burns  in  oxygen  with  dazzling  scintillations. 

Since  all  common  cases  of  burning  require  the  presence 
of  oxygen,  the  gas  is  said  to  support  combustion. 

~^   f "  --  0  3 

26.  Slow  Oxidation.  —  Oxidation  is  not  always  accom- 
panied by  light  or  even  by  noticeable  heat.  Thus,  when 
iron  rusts  (Fig.  11),  it  slowly  combines  with  oxygen; 


KINDLING    TEMPERATURE 


25 


when  wood  decays,  the  materials  produced  are  nearly  the 
same  as  are  formed  when  it  burns.  The  total  amount  of 
heat  is  the  same  in  both  cases,  but  in  the  decay  the  change 
takes  so  long  a  time  that  there  is  no  appreciable  change 
of  temperature.  A  match  gently  rubbed  in  the  dark 
appears  luminous  without  flaming.  Such  changes  as  rust- 
ing and  decay  are  termed  slow  oxidation.  As  distinguished 
from  burning,  slow  oxidation  is  the  combination  of  a  sub- 
stance with  oxygen  without  the  accompaniment  of  noticeable 
light  or  Iwat. 

27.  Kindling  Temperature.  —  We  know  that  some  sub- 
stances burn  more  easily  than  others  ;  heat  must  be 
applied  to  raise  them  to  the  tempera- 
ture at  which  they  take  fire  and  begin 
to  burn.  This  kindling  temperature 
varies  with  different  substances  ;  the 
kindling  temperature  of  phosphorus  is 
but  little  above  the  ordinary  laboratory 
temperature,  but  the  temperature  pro- 
duced by  the  burning  is  much  higher. 
If  the  burning  material  is  a  good  con- 
ductor, as  iron,  the  heat  is  conducted 
away  so  rapidly  that  the  temperature 
falls  below  the  kindling  temperature  and 
the  fire  goes  out.  Similarly,  gas  lighted 
above  an  iron  gauze  (a,  Fig.  12)  does  not  catch  fire  below  the 
gauze,  because  the  heat  of  the  flame  is  conducted  away  by 
the  iron.  When  the  material  is  in  small  pieces,  or  is  pow- 
dered, there  is  more  surface  exposed  to  the  oxygen,  so 
that  the  burning  can  proceed  more  rapidly ;  thus,  finely 
divided  iron  will  burn  when  sprinkled  into  •  a  Bunsen 
flame,  since  there  is  a  large  surface  exposed,  and  there  is 
no  large  mass  to  withdraw  the  heat.  In  the  case  of  iron, 


FIG.  12. 


26  OXYGEN 

the  oxide  produced  is  a  solid  which  remains,  and  may 
cover  the  iron  and  prevent  its  coming  in  contact  with  the 
oxygen,  thus  stopping  further  action.  Iron  is  artificially 
coated  with  a  thin,  regular  film  of  one  of  its  oxides  (§  405) 
to  protect  the  sheet  against  rusting.  Iron  so  protected  is 
known  as  Russia  iron. 

28.  Spontaneous  Combustion.  —  Many  oils,  such  as  are  used 
in  paints,  absorb  oxygen.     Linseed  oil  absorbs  oxygen  and 
forms  a  tough,  resinous  substance,  the  skin  seen  on  the 
surface  of  paint.     On  painted  surfaces,  this  skin  holds  the 
coloring  matter  and  protects  the  material  beneath.     The 
heat  generated  in  its  formation  is  dissipated  in  the  air. 
If  rags  or  waste,  greasy  with  such  oils,  are  left  lying  about, 
oxidation  takes  place,  and  since  the  materials  are  usually 
poor  conductors  and  their  form  prevents  sufficient  circula- 
tion of  the  air  to  keep  them  cool,  the  heat  does  not  escape, 
but  accumulates  until  the  temperature  rises  high  enough 
for  the  stuff  to  take  fire.     Coal  dust  in  coal  bunkers  often 
becomes  ignited  in  this  way.     Such  cases  of  burning  are 
often  called  spontaneous  combustion.    Spontaneous  combus- 
tion is  an  active  burning  started  by  the  accumulation  of  the 
heat  of  a  slow  oxidation.     It  is  especially  liable  to  occur  in 
poorly  ventilated  places  with  greasy  cloths  and  waste,  such 
as  are  used  about  machinery. 

29.  The  Bunsen  Burner.  —  This  burner  is  a  device  for  ad- 
justing the  proportions  of  fuel  gas  and  air  so  as  to  get  the 
combustible  mixture  giving  the  hottest  flame.     The  bunsen 
burner  was  the  first  successful  device  for  efficiently  utilizing 
gas  for  heating  and  its  principle  is  employed  in  all  gas 
heaters. 

When  the  burner  is  in  use,  gas  enters  the  barrel  through 
the  spud  (Fig.  13),  and  mixes  with  a  supply  of  air  partially 


Robert  Wilhelm  Bunsen  (1811-1899)  was  born  in  Gbttingen 
and  educated  in  its  university.  He  served  as  professor  in  several 
German  universities.  At  Heidelberg  he  had  a  career  of  nearly 
fifty  years  as  a  great  teacher  and  brilliant  investigator.  His  re- 
searches led  to  the  acceptance  of  the  idea  of  radicals  existing  in 
compounds.  Many  of  his  simple  and  efficient  laboratory  devices 
are  in  use  to-day,  notably  the  Bunsen  burner.  Bunsen  may  be 
regarded  as  the  founder  of  modern  gas  analysis.  His  greatest 
work  was  the  discovery,  with  Kirchhoff,  of  spectrum  analysis. 
This  proves  useful  in  the  detection  of  known  elements,  and  has 
led  to  the  discovery  of  new  ones.  By  its  means  Bunsen  found 
caesium  and  rubidium. 


THE  BUN  SEN  BURNER 


27 


sufficient  for  complete  combustion.     The  mixture  rises  to 

the  top  of  the  barrel,  where  it  is  ignited,  drawing  an 

additional    supply    of    oxygen 

from  the  surrounding  air.     The 

air  enters  the  holes  at  the  base 

of  the  barrel  because  the  gas  as 

it  issues  from  the  spud  at  a  high 

speed  causes  a  partial  vacuum  in 

the  barrel,  which  the  air  rushes 

in  to  fill. 

The  supply  of  gas  entering 

the  barrel  is  regulated  by  vary- 
ing the  size  of  the  opening  in 

the  supply  pipe.     The  supply  of 

air  is  regulated  by  turning  the 

ring  or  collar  so  as  to  vary  the 

size  of  the  holes  through  which 

the  air  enters  the  barrel.     If  the 

gas  pressure  is  low,  the  mixture 

of  gas  and  air  may  burn  down- 
ward more  rapidly  than  it  issues  from  the 
barrel.  In  this  case  the  flame  strikes  back 
to  the  spud,  where  incomplete  combustion 
takes  place.  This  produces  a  disagreeable 
odor.  Sometimes  the  base  becomes  suffi- 
ciently hot  to  melt  the  rubber  hose,  and 
the  escaping  gas  catches  fire. 

The  extreme  tip  of  the  outer  flame 
causes  many  substances  to  oxidize  when 
they  are  heated  in  it,  and  is  consequently 
called  the  oxidizing  flame.  The  portion 
of  the  flame  having  the  highest  temperature 

is  just  above  the  inner  cone  (Fig.  14). 

The   combustion   in   the    bunsen  flame    is  more   rapid 


FIG.  13.  —  SECTION  OF  BUNSEN 
BURNER. 


FIG.  14. 


28  OXYGEN 

than  that  in  the  ordinary  gas  flame,  since  the  fuel  does 
not  get  far  from  the  burner  before  burning.  Therefore, 
the  flame  is  smaller  and  for  this  reason  hotter.  It  is  not 
luminous,  owing  to  the  rapid  and  complete  burning  and 
to  the  dilution  of  the  materials  by  the  nitrogen. 

30.  Occurrence  of  Oxygen.  —  Oxygen  is  the  most  abun- 
dant  element :  about   one  half   of  the  solid   crust  of  the 
earth,  eight  ninths  of  the  water,  and  one  fifth  of  the  air,  is 
oxygen.     Limestone,  marble,  clay,  quartz,  and  sand  are 
nearly  half  oxygen,  and  it  comprises  a  large  proportion  of 
animal  and  vegetable  matter. 

31.  Oxygen  in  Relation  to  Life. — All  animals  need  oxy- 
gen for  the  carrying  on  of  their  life  processes.     The  air 
supplies  this  needed  oxygen  to  land  animals,  while  fishes 
obtain  it  from  the  dissolved  oxygen  which  water  absorbs 
from  the  air.     The  oxygen  is  taken  in  during  the  process 
of  breathing,  absorbed  by  the  blood,  and  carried  tq  all 
parts    of    the    body.       The    various    tissues    are    slowly 
oxidized,   heat    being    liberated    by    the   action.       It   is 
this  heat  which  keeps  the  bodies  of  the  higher  animals 
continually    warmer    than    the    surrounding    air.       One 
of   the  chief  products  of   this  oxidation  is  carbon  diox- 
ide, which  is  carried  by  the  blood  to  the  lungs  and  there 
exhaled. 

Plants  feed  on  carbon  dioxide,  which  they  absorb  from 
the  air  through  their  leaves.  The  carbon  of  this  com- 
pound is  retained  in  the  tissues  of  the  plants,  but  the 
oxygen  for  the  most  part  is  returned  to  the  air.  Thus 
plants  and  animals  mutually  assist  in  keeping  the  quan- 
tity of  oxygen  in  the  air  constant.  Plants  also  inhale  a 
small  quantity  of  oxygen  directly  from  the  air,  and  exhale 
a  little  carbon  dioxide. 


OZONE  29 

32.  Ozone.  —  If  electric  sparks  are  passed  through  oxy- 
gen, or  better,  if  it  be  subjected  to  a  "  silent  discharge  " 
of  electricity,  it  is  changed  to  another  form  of  oxygen, 
which  is  more  active,  and  which  has  the  irritating  smell 
noticeable  where  electrical  machinery  is  working.  This 
form  of  oxygen  is  known  as  ozone.  Ozone  is  also 
produced  by  the  slow  oxidation  of  phosphorus  in  moist 
air. 

When  ozone  is  heated  to  270°  C.  it  is  changed  to  oxygen, 
two  volumes  of  ozone  yielding  three  volumes  of  oxygen, 
so  that  the  ozone  is  one  and  a  half  times  as  dense  as 
oxygen. 

Silver,  which  is  not  affected  by  ordinary  oxygen,  is 
rapidly  darkened  (oxidized)  by  ozone.  Many  colors  are 
bleached  by  it. 

Improved  devices  for  the  production  of  electricity  have 
cheapened  the  cost  of  ozone,  so  that  it  is  used  for  purify- 
ing the  water  supply  of  large  cities,  as  Paris  and  Petrograd. 
The  ozone  is  produced  by  electric  discharges  in  special  ap- 
paratus known  as  ozonizers,  and  then  allowed  to  bubble 
up  through  long  cylinders,  to  which  water  is  admitted  at 
the  top.  These  streams  of  minute  bubbles  of  ozone  destroy 
all  forms  of  bacterial  life. 

Recent  experiments  have  used  ozone  for  the  purification 
of  the  air  of  school  rooms  and  of  places  for  public  as- 
semblage. Although  there  was  no  doubt  as  to  the  germi- 
cidal  action  of  the  ozone  and  its  removal  of  objectionable 
odor,  the  results  in  other  ways  were  not  altogether  satis- 
factory. 

The  atmosphere  sometimes  contains  a  small  amount  of 
ozone  near  the  seashore  and  in  the  open  country.  The 
bleaching  of  flax  and  linen  by  exposing  the  goods  on  the 
grass  in  the  early  morning  has  been  attributed  to  the 
ozone  dissolved  in  the  dew. 


30  OXYGEN 

SUMMARY 
Oxygen  is  prepared  by  : 

(a)  decompositon  of  mercuric  oxide  ; 

(b)  decomposition'  of  potassium  chlorate; 

(c)  electrolysis  of  water. 

Oxygen  is  1  .  1  times  as  heavy  as  air.     Liquid  oxygen  ooils  at 
-  182°  and  solidifies  below  -218°. 

Oxygen  combines  with  nearly  all  other  elements. 

An  oxide  is  a  compound  of  oxygen  and  another  element. 

A  catalytic  agent  is  a  material  which  aids  chemical  action  with- 
out itself  being  permanently  changed. 

Combustion  is  a  chemical  action  in  which  heat  and  light  are 

evolved. 

1 

Oxidation  is  the  combination  of  a  substance  with  oxygen. 

Ordinary  burning  is  an  oxidation  accompanied  by  noticeaoie 
heat  and  light. 

Slow  oxidation  is  the  combination  of  a  substance  with  oxygen 
without  the  accompaniment  of  noticeable  light  or  heat. 

The  kindling  temperature  of  a  substance  is  the  lowest  tempera- 
ture at  which  it  takes  fire  and  burns. 

Ozone  is  a  more  active  form  of  oxygen. 


EXERCISES 

1.  How   would  the  production   of  oxygen   be   affected  if 
potassium  chlorate  were  heated  without  a  catalytic  agent  ? 

Jj  '»'  p     //I  isQ'CW'  i&f  !  •ft'L-'    '/2xt^f--^2--C.  •    *W^lf/P(/'r,,{JJ^,&    i.    y.£--#  7    f.i   r.2.-'  'I 

2.  How  would  you  prove  that  water  from  a  stream  or  a  pond 
contains  dissolved  oxygen  ? 


EXERCISES  31 

3.  Name  the  product  formed  by  burning  each  of  the  follow- 
ing :  carbon,  iron,  sulphur,  tin,  magnesium,  and  phosphorus. 

4.  What  is  ordinary  burning  ? 

5.  What  would  happen  if  a  lighted  candle  were  lowered 
into  a  jar  of  oxygen  ?     Why  ? 

6.  Why  does  the  throwing  of  a  rug  around  a  burning  dress 
extinguish  the  flame  ? 

7.  Why  should  not  the  term  combustion  be  applied  to  a 
case  of  slow  oxidation  ? 

8.  Explain  the  successive  use  of  paper,  wood,  and  coal  in 
making  a  coal  fire. 

9.  Explain  why  polishing  stoves  prevents  rusting. 

10.  Explain  why  a  candle  goes  out  if  a  wire  gauze  is  slowly 
lowered  till  it  touches  the  wick. 

11.  Why  may  a  spark  in  a  flour  mill  produce  an  explosion  ? 

12.  Give  a  practical  illustration  of  putting  out  a  fire  (a)  by 
lowering  the  temperature  of  the  burning  material  below  its 
kindling  point ;  (6)  by  the  removal  of  the  combustible  material ; 
(c)  by  cutting  off  the  supply  of  oxygen. 

13.  State   the   conditions   necessary  for  spontaneous   com- 
bustion. 

14.  Why  are  metal  cans  provided  for  the  oily  waste  in  wood- 
turning  shops  ? 

15.  Why  should  not  greasy  cloths  be  thrown  into  a  closet  ? 

16.  Name  two  gases  in  the  air  that  are  required  by  plants  ? 
Which  in  the  larger  amount  ? 

17.  Account  for  the  peculiar  odor  in  the  air  after  a  thunder- 
storm. 

18.  Why  is  ozone  used  for  the  purification  of  water  ? 

19.  Why  does  blowing  extinguish  a  candle  ? 


32 


OXYGEN 


20.  Why  does  blowing  on  a  fire  make  it  burn  more  brightly  ? 

21.  In  order  to  find  the  per  cent  of  oxygen  in  air,  the 
oxygen  was  absorbed  by  means  of  phosphorus,  and  the  follow- 
ing data  were  obtained : 


WITH  OXYGEN 

OXYGEN 
EEMOVED 

99.8  c.c. 

77.0  c.c. 

24° 

19° 

Barom.G'ter     

763  mm. 

750  mm. 

The  air  stands  over  water,  and  the  levels  are  adjusted  in 
reading  both  volumes.     Calculate  the  per  cent  of  oxygen. 


CHAPTER   IV 

HYDROGEN 

33.  Preparation  by  Electrolysis  of  Water.  —  If  the   two 

wires  from  a  battery  be  placed  in  pure  water,  it  will  be 
found  that  practically  no  current  passes.  Water  is  a  very 
poor  conductor  of  electricity.  If  a  small  quantity  of  sul- 
phuric acid  is  added  to  the  water,  the  solution  is  a  good 


FIG.   15.  —  ELECTROLYSIS  OF  WATER. 
a,  platinum  electrode ;  b,  platinum  wire  fused  through  glass. 

conductor.  During  the  passage  of  the  current,  bubbles 
form  at  the  ends  of  the  wires;  at  the  positive  electrode 
(anode)  small  bubbles  of  oxygen  appear;  at  the  negative 
electrode  (cathode)  there  is  a  rapid  evolution  of  hydrogen 
(Fig.  15).  If  the  volumes  of  the  gases  be  compared,  it 
will  be  found  that  there  has  been  set  free  twice  as  much 

33 


34  HYDROGEN 

hydrogen  as  oxygen.  At  the  end  of  the  experiment,  the 
sulphuric  acid  is  found  unchanged  in  amount,  though 
some  of  the  water  has  disappeared.  Another  catalytic 
agent,  for  example,  potassium  hydroxide,  sodium  hydrox- 
ide, or  sodium  sulphate,  might  be  used  in  place  of  the 
sulphuric  acid.  Commercially,  potassium  hydroxide  is 
used.  The  electrolysis  has  converted  a  part  of  the  water 
into  oxygen  and  hydrogen,  and  the  volume  of  the  gases 
formed  is  very  great  compared  with  the  volume  of  the 
water  decomposed.  The  chemical  change  may  be  briefly 
represented  by  the  word  equation : 

water  — >-  hydrogen  +  oxygen. 

The  arrow  in  such  an  expression  is  to  be  read  yields,  and 
the  plus  sign  is  to  be  read  and. 

34.  Action  of  Metals  on  Water.  —  If  a  piece  of  potassium 
is  placed  on  water,  it  skims  back  and  forth  over  the  sur- 
face, decomposing  the  water  so  rapidly  that,  if  a  large 
piece  of  the  metal  is  used,  the  action  is  dangerously  vio- 
lent. A  great  deal  of  heat  is  generated,  so  that  the 
hydrogen  is  set  on  fire  (Fig.  16).  When  sodium  is 
used,  although  the  action  is  very  rapid,  the  heat  generated 
is  not  usually  sufficient  to  ignite  the  hydrogen  unless  the 
water  is  warm,  or  the  sodium  is  prevented  from  moving 
on  the  surface  of  the  water. 

The  metal  sets  free  only  one  half  of  the  hydrogen  of  the 
water,  and  combines  with  the  remaining  half  and  with  all 
of  the  oxygen,  to  form  the  hydroxide  of  the  metal.  The 
metallic  hydroxide  formed  dissolves  in  the  water  in  the 
vessel.  The  following  word  equations  may  be  used  to 
represent  the  reactions  : 

potassium  +  water  — *-  potassium  hydroxide  +  hydrogen 
sodium  -f-  water — >- sodium  hydroxide  +  hydrogen. 

-"?     fy  HJ.t- .  &* 


REPLACEMENT  IN  ACIDS   BY  METALS 


35 


Some  of  the  other  metals  will  also  react  with  water. 
When  calcium  is  used,  the  action  is  quiet,  and  not  all  of 
the  calcium  hydroxide  dissolves.  Magnesium  will  react 
rapidly  only  when  the  water  is  hot. 


FIG.  16.  —  POTASSIUM  ON  WATER. 


If  steam  is  passed  through  a  heated  pipe  filled  with  iron 
nails,  an  abundant  supply  of  hydrogen  can  be  obtained. 
The  oxygen  of  the  steam  combines  with  the  iron,  accord- 
ing to  the  equation: 

iron  +  water  (steam)  — >-  iron  oxide  4-  hydrogen. 

35.  Replacement  in  Acids  by  Metals.  —  In  the  seventeenth 
century,  Paracelsus  observed  that  when  iron  dissolved  in 
an  acid  a  gas  was  evolved.  All  acids  contain  hydrogen 
that  can  be  exchanged  for  a  metal,  and  in  a  number  of 
instances  the  hydrogen  is  liberated  and  can  be  obtained 


36 


HYDROGEN 


free.  Since  the  reaction  takes  place  at  ordinary  tem- 
peratures and  can  be  easily  controlled,  the  most  conven- 
ient method  of  preparing 
small  quantities  of  hydrogen 
is  to  add  a  water  solution  of 
sulphuric  acid  to  zinc  (Fig. 
17).  While  hydrogen  is  set 
free  during  the  reaction,  the 
zinc  combines  with  the  re- 
maining part  of  the  sul- 
phuric acid  and  forms  a  new 
FIG.  17.  — HYDROGEN  GENERATOR.  compound,  zinc  sulphate, 
which  remains  dissolved  in  the  liquid  in  the  generator: 

sulphuric  acid  +  zinc  — >^  zinc  sulphate  -f  hydrogen. 


[  hydrogen 
{  sulphur 
[oxygen 


I  zinc 
(  sulphur 
[ oxygen 


Sulphuric  acid  and  zinc  sulphate  are  compounds,  and 
the  words  printed  in  small  letters  under  each  indicate  of 
.what  elements  it  is  composed.  The  rapidity  of  the  action 
depends  on  the  temperature,  the  concentration  of  the  acid 
solution,  the  surface  of  the  metal  exposed,  and  the  purity 
of  the  materials.  Concentrated  sulphuric  acid  should  be 
diluted  with  from  four  to  six  times  its  volume  of  water. 
A  catalytic  agent,  for  example,  carbon  or  copper,  must 
be  in  contact  with  the  zinc.  Commercial  zinc  is  generally 
sufficiently  impure  to  give  good  results. 

Other  metals  besides  zinc  and  other  acids  besides  sul- 
phuric acid  may  be  used  for  the  preparation  of  hydrogen, 
but  it  is  far  from  true  that  free  hydrogen  can  be  obtained 
by  the  reaction  between  any  acid  and  any  metal.  Dilute 
solutions  of  either  sulphuric  or  hydrochloric  acid  are  usu- 
ally employed,  with  either  zinc  or  iron. 


COMBUSTIBILITY  37 

36.  Physical  Properties.  —  Hydrogen  is  a  gas  without 
color,  taste,  or  odor.     When  commercial  zinc  and  acid  are 
used  in  its  preparation,  impurities  are  carried  along  with 
the  hydrogen,  giving  it  a  peculiar,  disagreeable  odor.     If 
iron  is  used  instead  of  zinc,  the  unpleasantness  of  the 
odor  is  more  noticeable.     Hydrogen  is  scarcely  soluble  in 
water.     It  is  the  lightest  substance  known ;    1  liter  of 
hydrogen  weighs  0.09  of  a  gram.     The  rate  of  escape  of 
gases  through  small  apertures  (effusion  of  gases)  varies 
inversely  as  the  square  roots  of  their  densities.     Hydro- 
gen, being  the  lightest  gas,  escapes  more  rapidly  than  any 
other.     A  small  rubber  balloon  filled  with  hydrogen  col- 
lapses more  rapidly  than  a  similar   balloon   filled  with 
illuminating  gas. 

Certain  metals,  as  platinum  and  palladium,  have  the 
power  of  absorbing  large  volumes  of  hydrogen.  The 
hydrogen  is  expelled  when  the  metal  is  warmed.  Such 
an  absorption  of  gas  by  a  solid  is  called  occlusion.  While 
the  gas  is  being  absorbed,  considerable  heat  is  set  free, 
and,  if  oxygen  is  present,  the  hydrogen  may  ignite.  The 
occluding  action  of  such  a  metal  is  utilized  in  self-lighting 
gas  burners  and  cigar  lighters. 

Hydrogen  has  been  liquefied  and  solidified.  The  liquid 
is  one  fourteenth  as  dense  as  water,  and  is  the  lightest 
liquid  known. 

CHEMICAL  PROPERTIES 

37.  Combustibility.  —  The  most  important  chemical  prop- 
erty of   hydrogen  is  its   combustibility.     Cavendish,  in 
1783,  showed  that  hydrogen  burning  in  air  formed  water. 
The  water  formed  by  the  combustion  of  hydrogen  usually 
passes  off  unnoticed  as  steam,  but  it  may  be  condensed  on 
a  cool  surface  (Fig.  18).     The  flame  of  hydrogen  is  blue, 
almost  invisible  in  the  daylight,  and  is  very  hot.     Hydro- 


HYDROGEN 


gen  in  burning  gives  as  much  heat  as  about  5  times  its 
weight  of  coal. 

If  hydrogen  and  oxygen  are  mixed,  and  the  mixture  is 
raised  to  its  kindling  temperature,  or  if  an  electric  spark 
is  passed  through  the  mixture,  combustion  takes  place 
throughout  the  entire  mass  almost  instantaneously,  pro- 
ducing a  sudden  increase  in  volume.  Such  a  rapid  com- 


FIG.  18.  —  FORMATION  OF  WATER. 

a,  hydrogen  generator  ;  b,  jet  of  burning  hydrogen  ;  c,  metallic  cone  ; 
d,  glass  condenser  ;  e,  string  along  which  condensed  water  runs  into 
graduate. 

bustion,  accompanied  by  a  sudden  increase  in  pressure,  is 
termed  an  explosion.  A  jet  of  oxygen  can  be  made  to 
burn  in  hydrogen,  thus  showing  that  the  two  gases  take 
equal  part  in  the  action. 

•  "  9 


I 


38.  Reducing  Action.  —  Hydrogen  will  take  oxygen  from 
many  oxides  when  they  are  heated  in  it  (Fig.  19),  forming 
water  (steam)  and  leaving  the  metal  free  : 


copper  oxide  +  hydrogen 

•/- 


water  +  copper. 


USES 


39 


This  process  of  taking  oxygen  away  from  a  substance 
is  called  reduction,  and  substances  that  take  oxygen  away 
are  called  reducing  agents.  As  the  hydrogen  is  oxidized 
in  the  process,  we  see  that  oxidation  and  reduction  go  on 
together  and  are  opposite  processes.  Hydrogen  is  one  of 
the  most  energetic  reducing  agents.  Energy  equivalent 
to  about  3800  calories  of  heat  must  be  used  to  decom- 


FIG.  19.  —  REDUCTION  OF  HOT  COPPER  OXIDE  BY  HYDROGEN. 
a,  hydrogen  generator ;  b,  drying  tube  ;  c,  test  tube  ;  d,  copper  oxide. 

pose  one  gram  of  water.  The  amount  of  heat  given  off 
during  the  formation  of  water  explains  the  stability  of 
water. 

39.  Uses. — The  low  density  of  hydrogen  permits  its 
use  in  balloons.  The  high  temperature  of  the  flame  is 
used  in  the  oxy-hydrogen  blowpipe.  This  consists  of 
two  tubes  as  shown  in  Fig.  20.  The  hydrogen  passes 


40  HYDROGEN 

through  the  outer  tube  and  is  lighted  at  the  tip ;  then  the 
oxygen  is  turned  on  through  the  inner  tube.  As  the 
gases  are  supplied  under  pressure,  a  blast  is  formed  which 
gives  an  intense  heat.  This  flame  is  used  to  melt  plati- 
num and  other  refractory  materials,  such  as  aluminum 
oxide,  during  the  manufacture  of  artificial  rubies  and  sap- 
phires. When  a  stick  of  quicklime  is  placed  in  the  tip  of 
the  flame,  it  does  not  melt,  but  becomes  white-hot,  giving 

an    intense   white    light. 

y     '  =^\     This    is    known    as    the 

)xyge°   J  |~  Drummond,  lime,  or  cal- 

cium light. 
|Hydrogen  The  process  of  joining 

FIG.  20.- OXY-HYDROGEN  BLOWPIPE.       sheets    of     lead»    edge    to 

edge,  known  as  lead- 
burning,  consists  in  laying  the  sheets  in  the  position 
desired  and  melting  the  edges  together  with  a  hydrogen 
flame. 

Ordinary  water  gas  is  made  by  blowing  steam  through 
a  mass  of  incandescent  anthracite  coal,  or  coke.  It  con- 
tains 50%  of  hydrogen  and  is  suitable  for  burning  to 
produce  heat,  but  the  straight,  or  unenriched,  water  gas  has 
no  practical  value  as  an  illuminant.  Nearly  three  fourths 
of  the  illuminating  gas  used  in  this  country  is  enriched 
water  gas  (§  335)  and  contains  about  38%  of  hydrogen. 

40,  Hydrogenation  of  Oils.  —  Large  quantities  of  hydro- 
gen are  consumed  in  the  hydrogenation  of  oils.  In  the 
presence  of  a  suitable  catalytic  agent,  for  example,  finely 
divided  nickel  (obtained  by  the  reduction  of  nickel  oxide), 
hydrogen  enters  into  combination  with  cottonseed  oil  and 
converts  it  into  a  product  resembling  lard.  This  product 
is  edible  and  is  sold  extensively  as  a  lard  substitute.  By 
a  similar  process,  fish  oil  can  be  made  to  lose  its  disagree- 


EXERCISES  41 

able  odor  and  be  converted  into  a  fat  suitable  for  use  in 
making  hard  soap. 

SUMMARY 

Hydrogen  is  commonly  prepared  by : 

(1)  the  electrolysis  of  water  (commercial  method)  ; 

(2)  the  reaction  between  water  and  a  metal ; 

(3)  replacement  in  an  acid  by  a  metal.     This  is  the 

most  convenient  method. 

A  liter  of  hydrogen,  under  standard  conditions,  weighs  0.09 
gram.  A  liter  of  water  at  20°  dissolves  18.2  c.c.  of  hydrogen. 
Liquid  hydrogen  boils  at  -  252.5°  and  solidifies  at  -  259°. 

Hydrogen  burns  in  oxygen  or  air,  forming  water.  It  is  a 
powerful  reducing  agent.  The  chief  uses  of  hydrogen  are  for 
balloons,  for  fuel,  and  for  the  hydrogenation  of  oils. 


EXERCISES 

1.  What   would  be   the  result  of  collecting  together  the 
gases  formed  by  the  electrolysis  of  water  and  applying  a  light 
to  the  mixture  ?  J%/A^ 

2.  Would   you  use  water   or  sand  to  extinguish  burning 
sodium?     Why? 

3.  Would  you  use  zinc  or  iron  for  making  hydrogen  to  fill 
a  large  balloon  ?     Why  ? 

4.  What   becomes    of  the  product,  other  than  hydrogen, 

formed  when  zinc  and  sulphuric  acid  react  ?  fa 
<'•  }ii*{i''vw    0&ts4ffa~£vt     /••  w^JEwKI. ' 

5.  Is  wate/an  oxide  ? 

6.  How  would  a  soap  bubble  behave  if  filled  with  hydrogen 
instead  of  air  ?  j? - 

7.  Why  do  toy  balloons  filled  with  hydrogen  collapse  in  a 
short  time  ? 

~rf     /.'      *r       S^l'l+f     ^(S,  '-'.-'^ 


42  HYDROGEN 

8.  Would  a  bottle  of  hydrogen,  closed  with  an  ordinary 
cork,  remain  full  after  standing  overnight  ?    ' 

9.  Would  a  bottle  of  hydrogen  remain  full  if  left  inverted 
overnight  with  its  mouth  under  water  ? 

10.  Why  must   all  the  air  be  expellld  from  a  hydrogen 
generator  before  the  gas  is  lighted  at  the  end  of  the  delivery 
tube? 

11.  Should  vessels  containing  hydrogen  be  kept  mouth  up- 
ward or  mouth  downward  ? 

12.  Why  would  pure  hydrogen  not  make  a  good  illuminating 
gas? 

13.  Could  hydrogen  be  substituted  for  illuminating  gas  in 
an  ordinary  gas  stove  ? 

14.  What  is  formed  when  iron  oxide  is  heated  in  a  current 
of  hydrogen  ?    tf/t 

15.  Would  a  Welsbach  burner  supplied  with  hydrogen  give 
light? 

16.  W^y  is  hydrogen  called  a  reducing  agent  ? 

£%%L«     4~~fati**/9L^v~Cu/    ..f  <i  <n,-i^     .'1-1. '„&:+(.•/ 

17.  What  is  lead  burning  ? 

18.  By  making  iise  of  hydrogen,  how  could  you  show  that 
air  contains  oxygen  ? 

19.  Mention  two  ways  in  which  the  cheap  production  of 
hydrogen  tends  to  decrease  the  cost  of  living. 


CHAPTER   V 


COMPOSITION  OF  -WATER  AND  COMBINING 
WEIGHTS 

41.  Analysis  and  Synthesis.  —  In  the  electrolysis  of  water, 
we  showed  that  water  could  be  separated  into  two  parts 
hydrogen  and  one  part  oxygen  by  volume.     Such  a  sep- 
aration is  called  an  analysis.     The  combining   of   these 
substances  is  called  a  synthesis  of  water. 

42.  Synthesis  by  Volume.  —  If  known  volumes  of  hydro- 
gen and  oxygen  are  introduced  into  a  tube  inverted  over 
mercury,  and  exploded  by  an        E 

electric  spark  between  plati- 
num wires  fused  through  the 
glass,  it  is  found  that  the  vol- 
umes of  the  gases  uniting  are 
two  volumes  of  hydrogen  to  one 
of  oxygen,  and  that  any  excess 
of  either  gas  is  left  unchanged. 
It  is  only  when  two  volumes 
of  hydrogen  are  mixed  with 
one  of  oxygen  that  the  two 
gases  totally  disappear.  A 
little  mist  is  seen  on  the  tube, 
which  is  the  moisture  formed, 
and  the  mercury  rises  and  fills 
the  tube.  This,  again,  shows 

that   water    consists    of    two    parts    hydrogen    and   one 
part    oxygen.      Another    form    of   apparatus    (Fig.    21)^ 

43 


44  COMPOSITION  OF   WATER 

differing  in  the  shape  of  the  tube  from  that  just  de- 
scribed, facilitates  the  adjustment  and  reading  of  the 
mercury  levels.  Additional  mercury,  if  needed,  can 
be  poured  through  the  open  arm  B,  and  an  excess 
can  be  drawn  off  through  the  lower  stopcock  D.  The 
gases  used  in  A  can  be  drawn  in  easily  through  the  three- 
way  stopcock  Q  shown  in  detail  at  JE.  If  the  tube  A  is 
provided  with  a  heating  device  so  that  the  temperature 
can  be  raised  above  100°  C.,  the  volume  of  the  steam  can 
be  measured.  If  the  measurements  are  made  at  the  same 
temperature  and  pressure,  it  will  be  found  that  the  volume 
of  the  steam  is  just  equal  to  the  volume  of  the  hydrogen. 


FIG.  22.  —  COMPOSITION  OF  WATER  BY  WEIGHT. 

a,  hydrogen  generator ;  b,  b,  drying  bottles  containing  concentrated  sul- 
phuric acid ;  c,  ignition  tube  containing  copper  oxide ;  d,  d,  apparatus 
for  collecting  water  formed. 

43.  Synthesis  by  Weight.  —  If  dry  hydrogen  is  passed 
over  a  weighed  quantity  of  copper  oxide  which  is  heated, 
steam  and  copper  result  (Fig.  22).  The  water  can  be 
collected  and  weighed  in  a  tube  containing  a  drying  agent. 

'iVfl -,//,->    c* 


John  Dalton  (1766-1844)  was  an  English  schoolmaster,  inves- 
tigator, and  mathematician.  Dalton's  work  led  up  to  the  funda- 
mental ideas  of  modern  chemistry. 

He  studied  rocks,  dew,  the  weather,  and  various  phenomena, 
notably  those  of  gases,  which  he  pictured  as  made  up  of  small, 
elastic  particles.  While  the  idea  of  atoms  was  not  original  with 
Dalton,  he  experimented  and  collected  data  which  showed  that  the 
facts  could  be  explained  by  what  we  now  call  the  atomic  theory. 

The  law  of  definite  proportions  and  the  law  of  multiple  propor- 
tions are  two  of  the  most  important  chemical  generalizations  stated 
by  Dalton  in  the  development  of  his  theory. 


COMBINING    WEIGHTS 


45 


The  weight  lost  by  the  copper  oxide  is  the  weight  of  the 
oxygen.  The  difference  between  the  weight  of  the  oxy- 
gen and  the  weight  of  the  water  formed  is  the  weight  of 
the  hydrogen. 

44.  Law  of  Definite  Proportions.  —  The  ratio  between  the 
weights  of   the   oxygen   and    hydrogen   is   found  to   be 
7.94  :  1.      This  relation  is  unvarying.       Experience   has 
shown  that  every  compound  has  a  definite  composition  by 
weight.     This  is  known  as  Dalton's  first  law,  or  the  law  of 
definite  proportions. 

45.  Combining  Weights.  —  Experience   has  shown   that 
the  knowledge  of  the  composition  by  weight  of  chemical 
compounds  is  very  useful.     For  example,  we  can  deter- 
mine what  weights  of  substances  are  needed  for  a  given 
chemical  action,  and  what  weight  of  the  products  will  be 
formed.     Moreover,  a  study  of  these  weights  reveals  some 
surprising  regularities.      Let  us   consider  a   few  simple 
cases.     In  the  table  below,  in  the  OXYGEN  column  is  given 
the  weight  of  oxygen  that  combines  with  one  part  by 
weight  of  the  substance  in  the  first  column.     Similarly 
the  columns  SULPHUR  and  CHLORINE  give  the  weights  of 
these  elements  that  combine  with  one  part  by  weight  of 
the  element  in  the  first  column. 


'J 

OXYGEN 

SULPHUR 

CHLORINE 

1  part  hydrogen  combines  with 
1  part  carbon      

^8.00  <W 
2.66 

/;  16.0 
5.33 

,     35.5 
11.8 

1  part  magnesium  

.666 

1.33 

2.96 

1  part  calcium     

.400 

.800 

1.77 

1  part  copper  ...         ... 

.251 

.502 

1.11 

1  part  zinc      

.246 

.492 

1.09 

1  part  mercury             .... 

.080 

.160 

.35 

1  part  silver  .              ...» 

.074 

.148 

.33 

46  COMPOSITION  OF   WATER 

The  numbers  vary  considerably,  and  there  seems  to  be 
little  order  about  them.  We  have  considered  one  part 
by  weight  of  each  material  in  the  first  column.  We  have 
used  eight  different  units;  a  unit  quantity  of  hydrogen, 
a  unit  quantity  of  carbon,  and  so  forth.  We  notice  that 
the  weights  in  the  sulphur  column  are  double  those  in  the 
oxygen  column  and  weights  in  the  chlorine  column  are 
nearly  4.44  times  the  oxygen  weights. 

This  suggests  the  value  of  reducing  all  the  ratios  to  a 
common  standard,  so  that  regularities  will  be  apparent  at 
a  glance.  Hydrogen  enters  into  combination  in  the  least 
part  by  weight  of  any  of  the  elements. 

Let  us,  therefore,  use  1  for  the  combining  weight  of 
hydrogen. 

If  we  took  1  part  by  weight  (1  pound,  1  gram,  or  1 
unit  of  any  kind)  of  hydrogen  and  combined  it  with 
oxygen,  it  would  require  8  parts  by  weight,  8  pounds, 
8  grams,  or  8  of  whatever  units  were  chosen. 

Now,  2.66  parts  of  oxygen  combine  with  1  part  of 
carbon,  so  8  parts  of  oxygen  are  needed  to  combine  with  3 
parts  of  carbon.  These  3  parts  of  carbon,  then,  will  com- 
bine with  1  part  of  hydrogen. 

In  the  same  manner  we  find  that  the  8  parts  by  weight  of 
oxygen  that  will  unite  with  1  part  of  hydrogen,  will  conu 
bine  with  20  parts  of  calcium,  or  31.8  parts  of  copper,  or 
32.7  of  zinc. 

The  16  parts  of  sulphur  that  combine  with  1  part  of 
hydrogen  will  combine  with  just  3  parts  of  carbon  (since 
5.33  parts  of  sulphur  combine  with  1  part  of  carbon),  or 
with  20  of  calcium,  or  with  31.8  of  copper. 

Similarly  we  can  find  the  weights  of  these  elements,  in 
the  first  column,  that  could  unite  with  the  35.5  parts  of 
chlorine  which  combine  with  1  part  of  hydrogen.  The 
weights  are  given  in  the  table  following. 


REACTING    WEIGHT 


47 


V 

OXYGEN 

SULPHUR 

CHLORINE 

1  part  hydrogen  will  combine  with 

8 
8 

16 
16 

35.5 
35.5 

12  parts  magnesium     .     .     .     .    ^ 
^0  parts  calcium 

8 
8 

16 
16 

35.5 
35.5 

31  8  parts  copper 

8 

16 

35.5 

8 

16 

35.5 

8 

16 

35.5 

8 

16 

35.5 

Thus  we  see  that  the  combining  number  is  found  to  be 
the  same  for  each  of  these  elements,  regardless  of  the  other 
element  in  the  compound.  Experiment  shows  that  3 
parts  of  carbon  will  combine  with  1  part  of  hydrogen 
and  that  20  grams  of  calcium  or  32.7  grams  of  zinc  are  re- 
quired to  liberate  1  gram  of  hydrogen  from  water  or  any 
other  hydrogen  compound.  From  this  it  appears  that 
each  element  enters  into  chemical  action  in  a  definite 
number  of  parts  by  weight,  and  if  we  establish  these 
numbers  on  a  relative  scale,  the  number  for  an  element  is 
the  same  in  all  its  compounds.  This  number  is  called  the 
equivalent  or  reacting  weight^®!  the  element. 

46.  Reacting  Weight.  —  It  is  found  that  such  a  number 
can  be  assigned  to  every  element.  The  number  is  found 
by  determining  the  number  of  parts  by  weight  of  the  given 
element  which  unite  with,  or  replace,  one  part  of  hydrogen, 
or  its  equivalent.  Thus  we  see  that  all  reacting  weights 
are  relative  numbers,  and  they  refer  or  relate  to  the  com- 
bining weight  of  hydrogen  which  is  taken  as  unity. 

It  frequently  happens  that  more  than  one  reacting  weight 
can  be  assigned  to  a  given  element.  For  instance,  oxygen 
combines  in  two  different  proportions  with  hydrogen, 


48  .  COMPOSITION  OF   WATER 

forming  two  different  compounds.  In  water  the  ratio  is 
8  to  1,  in  the  other  compound  the  ratio  is  16  to  1.  In 
such  cases,  one  reacting  weight  is  always  a  multiple  of  the  other. 

47.  Method  of  determining  Reacting  Weights.  —  The  re- 
acting weight  is  determined  by  an  analysis  of  the  hydrogen 
compound,  if  one  exists.  In  some  other  cases  the  value  is 
determined  by  finding  the  weight  of  the  element  that 
replaces  1  gram  of  hydrogen.  In  still  other  cases,  the 
number  expressing  the  weight  of  the  element  that  com- 
bines with  35.5  grams  of  chlorine  or  8  grams  of  oxygen  is 
taken  as  the  reacting  weight. 

SUMMARY 

The  composition  of  water  can  be  shown  by  analysis  and  by 
synthesis.  Two  volumes  of  hydrogen  unite  with  1  volume  of  oxy- 
gen to  form  2  volumes  of  steam. 

Water  consists  of  1  part  by  weight  of  hydrogen  combined  with 
8  parts  of  oxygen  ;  and,  since  it  always  has  this  composition,  it  illus- 
trates the  law  of  definite  proportions,  that  every  compound  has  a 
definite  composition  by  weight. 

The  number  of  parts  by  weight  of  an  element  which  react  with 
one  part  by  weight  of  hydrogen,  or  .its  equivalent,  is  called  the 
reacting  weight  of  that  element.  When  an  element  has  more  than 
one  reacting  weight,  the  numbers  expressing  these  weights  are 
always  multiples  of  the  smallest  number. 

EXERCISES 

1.  When  sugar  is  heated  sufficiently  to  char  it,  water  is 
driven  off.     What  two  elements  besides  carbon  must  sugar 
contain  ?    M 

2.  Why  does  a  thin  film  of  water  collect  on  the  inside  of  a 
lamp  chimney  when  the  lamp  is  first  lighted  ?     Why  does  the 
moisture  soon  disappear  ? 


EXERCISES  49 

3.  Dry  hydrogen  was  passed  over  heated  copper  oxide  and 
the  water  formed  was  absorbed  by  fused  calcium  chloride.     The 
following  results  were  obtained  : 

Wt.  of  copper  oxide  tube  before  the  experiment  .....    70  g. 

Wt.  of  copper  oxide  tube  after  the  experiment  ......     66  g. 

Wt.  of  calcium  chloride  tube  after  the  experiment  .  .  106.5  g. 
Wt.  of  calcium  chloride  tube  before  the  experiment  .  .  102  g. 
From  the  above  data  calculate  the  weight  composition  of  water.  - 

4.  15  c.c.  of  oxygen  were  collected  in  a  eudiometer  over 
mercury.     Dry  hydrogen  was  passed  into  the  eudiometer  until 
the  volume  of  the  mixed  gas  was  22.4  c.c.     A  spark  was  then 
passed  through  the  mixture.     What  gas  was  left  in  the  eudi- 
ometer ?fj  How  would  you  prove  your  answer  ?     What  would 
be  the  volume  of  the  remaining  gas  ? 

5.  Mention  three  ways  by  which  water  can  be  decomposed. 

/yyi&Z&tt    IT**   9trfrfo*    MfllfrU**}**  -<^t     a^tld-  ^ 

6.  Describe  an  experiment  that  you  could  perform  to  illus- 

trate the  law  of  definite  proportions.    , 

7.  How  many  grams  of  zinc  are  necessary  for  the  production, 
by  the  action  of  hydrochloric  acid  on  the  metal,  of  90  liters  of 
hydrogen  measured  under  standard  conditions  ?     (One  liter  of 
hydrogen  weighs  0.09  gram.)    £  ^  /  ^  • 


8.  What  does  the  analysis  of  water  show  its  composition  to 
be  by  volume  ?  2   /^#/^ 

l  ^rt^u^f*^-'          '  f  a 

9.  Mention  two  methods  for  the  synthesis  of  water.?*/; 


CHAPTER   VI 
WATER  AND  SOLUTION 

48.  Physical  Properties.  —  Pure  water  is  an  odorless 
liquid.  Small  quantities  appear  to  be  colorless,  although 
large  masses  show  a  distinct  blue  color.  Water  is  usually 
taken  as  the  standard  in  comparisons  of  physical  properties 
of  liquids  and  solids.  The  zero  of  the  Centigrade  ther- 
mometer registers  the  position  of  the  top  of  the  mercury 
column  when  the  thermometer  is  placed  in  melting  ice, 
and  since  a  pure  substance  on  being  warmed  always  melts 
at  the  same  temperature  as  that  at  which  it  would  solidify 
if  cooled,  the  zero  of  the  Centigrade  thermometer  is  the 
freezing  point  for  water. 

When  pure  water  is  heated  to  100°  C.  under  a  pressure 
of  760  mm.,  it  boils;  if  we  continue  to  apply  heat,  the 
temperature  does  not  rise  higher,  provided  the  steam  is 
allowed  to  escape.  The  heat  used  in  converting  water 
into  steam  is  known  as  the  heat  of  vaporization,  or  the 
latent  heat  of  steam ;  it  is  given  off  when  the  steam  con- 
denses. The  heat  used  in  changing  ice  to  water  is  known 
as  the  heat  of  fusion.  This  is  also  latent  heat,  as  it  is 
given  off  when  the  water  changes  back  to  ice. 

These  quantities  of  heat  are  commonly  measured  in  units 
known  as  calories.  The  calorie  is  the  quantity  of  heat  re- 
quired to  raise  a  gram  of  water  1°  Centigrade.  About  80 
calories  are  required  to  change  a  gram  of  ice  at  0°  C.  to 
water  at  0°  C.,  and  540  calories  are  required  to  change  the 
same  mass  of  water  at  100°  C.  to  steam  at  100°  C. 

so 


DISTILLA  TION 


51 


Both  the  freezing  and  boiling  temperatures  change  when 
the  pressure  changes;  increased  pressure  raises  the  boiling 
point  and  lowers  the  freezing  point,  in  both  cases  tending 
to  keep  it  in  the  liquid  form.  Any  dissolved  solid  acts  in 
the  same  way. 


FIG.  23.  —  LABORATORY  DISTILLATION. 

49.  Distillation.  —  All  natural  water  contains  dissolved 
-substances.  It  is  therefore  necessary  to  boil  water  and 
then  condense  the  steam  to  make  it  fit  for  chemical  use; 
this  process  is  called  distillation  (Fig.  23).  Solids  and 
liquids  with  boiling  points  much  higher  than  that  of  water 
are  left  behind,  as  the  temperature  of  the  steam  remains 
the  same  during  the  distillation.  Materials  having  lower 
boiling  points  than  water  are  distilled  before  or  with  the 
water ;  such  impurities,  ammonia  for  example,  are  found 
in  the  first  portion  of  the  condensed  steam,  and  this  is 
rejected. 

Distillation  consists  in  changing  a  liquid  to  a  gas  (vapor- 


52  WATER  AND   SOLUTION 

ization)    and  then  cooling  the  gas  so  that  it  becomes  a 
liquid  again  (condensation). 

50.  Steam.  —  Steam  is  water  in  the   gaseous  state ;  at 
ordinary  pressure  it  condenses  to  liquid  at  100°  C.  ;  if  the 
pressure  be  removed,  it  remains  in  the  gaseous  condition 
at  lower  temperatures.     The  volume  of  steam  is  about 
1600  times  that  of  the  water  from  which  it  was  formed. 

51.  Ice.  —  If   the  temperature  of  water  is  lowered  to 
0°  C.,   and  energy   removed,  it   solidifies  to   ice,   usually 
crystallizing  in  hexagonal  clusters  of  needles.     There  is 
considerable  expansion  during  the  solidification,  and  the 
density  of  the  ice  is  only  0.91  that  of  water. 

Water  requires  more  heat  to  raise  its  temperature  than 
do  most  substances  :  therefore  its  temperature  changes 
more  slowly  than  most  objects,  and  large  masses  of  water 
considerably  affect  the  climate  of  the  neighboring  land. 

52.  Solution.  —  The  most  important  property  of  water  is 
its  ability  to  dissolve  substances.     A  substance  is  said  to 
be  in  solution  in  a  liquid  when  it  is  distributed  uniformly 
through  the  liquid  in  a  state  of  such  fine  division  that  its 
particles  cannot  be  seen,  and  do  not  settle  out  on  standing. 
When  the  particles  are  visible,  the  substance  is  said  to  be 
in  suspension,  and  will  usually  settle  quickly.     A  liquid 
used  to  dissolve  a  substance  is  called  a  solvent ;  the  dis- 
solved  substance   is   termed   the  solute.     A  solution  is  a 
uniform  mixture  of  these,  which  does  not  conform  to  the 
law  of  definite  proportion.     A  solution  will  not  boil  at  the 
same  temperature  as  the  solvent,  nor  will  their  freezing 
points  be  the  same. 

Water  is  a  solvent  for  a  large  number  of  substances,  and 
this  use  is  most  important.  It  dissolves  both  gases  and 


SATURATION  53 

solids  and  mixes  with  many  liquids.  Liquids  which 
do  not  separate  but  form  a  uniform  mixture  when 
brought  together,  as  alcohol  and  water,  or  glycerine  and 
water,  are  said  to  be  miscible.  Kerosene  and  water  are 
nbn-miscible  liquids. 

53.  Saturation.  —  A  solution  is  not  a  definite  compound. 
A  small  portion  of  salt  may  be  dissolved  in  a  large  quan- 
tity of  water ;  such  a  solution  is  said  to  be  dilute.     In  a 
dilute  solution,  the  substance  is  as  uniformly  distributed 
in  all  parts  of  the  liquid  as  it  is  in  one  containing  a  much 
larger  proportion  of  the  dissolved  substance.     A  definite 
amount  of  water  will  dissolve  any  amount  of  a  given  solid 
up  to  a  fixed  quantity.     If  a  liter  of  water  at  20°  C.  is 
taken,  it  is  possible  to  dissolve  in  it  any  weight  of  salt  up 
to  360  grams.     When  the  water  has  dissolved  all  the  salt  it 
can  under  given  conditions,  it  is  said  to  be  saturated  with 
salt  at  the  temperature  mentioned.     A  similar  statement 
can  be  made  concerning  the  solubility  of  any  solid  in  any 
liquid.     When  any  solvent  has  dissolved  all  of  a  given 
solute  that  it  can,  under  definite  conditions,  it  is  said  to  be 
saturated  with  respect  to  that  substance  under  the  conditions 
named.      A   solution  saturated  with  one  substance  may 
dissolve   other   substances.     Thus,  water  saturated  with 
respect  to  salt  can  dissolve  saltpeter. 

54.  Relation  of  Solubility  to  Temperature.  —  The  solubility 
of  most  substances  is  decidedly  affected  by  the  temperature. 
Solids  are  usually,  but  not  always,  more  soluble  in  liquids 
at  high  than  at  low  temperatures.     Sugar,  alum,  and  salt- 
peter (Fig.  24)  are  more  soluble  in  hot  water  than  in  cold. 
Salt   dissolves   nearly  as  well   in   cold   as   in   hot  water 
(Fig.  25).     Calcium  hydroxide,  used  in  the  preparation  of 
limewater,  is  more  soluble  in  cold  water  than  in  warm. 

Unlike  solids,  the  solubility  of  gases  in  liquids  decreases 


54  WATER  AND  SOLUTION 

as  the  temperature  rises.  Ammonia  and  carbon  dioxide 
are  less  soluble  in  hot  water  than  they  are  in  cold.  Dif- 
ferent substances  differ  very  much  in  their  solubility  in  a 


1 


FIG.  24.  —  RELATIVE  SOLUBILITY  OF  SALTPETER  IN  COLD  AND  IN  HOT  WATER. 

given  solvent,  and  different  solvents  differ  in  their  power 
to  dissolve  the  same  substance. 

55.  Relation  of  Solubility  to  Pressure. —  While   pressure 
has  little  effect  on  the  solubility  of  solids,  it  has  a  decided 
effect  on  the  solubility  of  gases.     The  weight  of  a  gas  dis- 
solved in  a  given  volume  of  a  liquid  is  directly  propor- 
tional to  the  pressure. 

56.  Freezing  Mixtures.  —  There    are    important    energy 
changes    during    solution.     When    a    solid   is    dissolved, 
energy  is  absorbed  and  there  is  generally  a  fall  in  tem- 
perature.    This   is   made    use    of   in    freezing   mixtures. 
When  ice  and  salt  are  mixed,  some  of  the  ice  melts  and 
the  salt  dissolves  in  the  water.     Both  processes  result  in 


SUPERSATURATION  55 

the  absorption  of  heat,  and  the  temperature  of  the  mix- 
ture falls  considerably  below  the  freezing  point  of  pure 
water.  When  equal  parts  of  ammonium  nitrate  and 


FIG.  25.  —  RELATIVE  SOLUBILITY  OF  SALT  IN  COLD  AND  IN  BOILING  WATER. 

water  are  mixed,  at  0°  C.,  the  temperature  falls  to  —  15°  C. 
In  the  freezing  of  ice  cream,  the  heat  necessary  to  melt 
the  ice  and  dissolve  the  salt  is  mainly  taken  from  the 
inner  can  and  its  contents. 

57.  Supersatnration.  —  If  a  solution  is  saturated  at  a  high 
temperature  and  then  allowed  to  cool  slowly  without  any 
disturbance,  it  will  often  cool  to  a  lower  temperature  with- 
out depositing  any  of  the  substance  dissolved  (Fig.  26,  a). 
But  if  a  particle  of  the  dissolved  substance  is  dropped  into 
the  solution,  a  sudden  crystallization  takes  place,  accom- 
panied by  an  evolution  of  heat  (Fig.  26,  6,  c?,  d~).  Such  a 
solution  is  said  to  have  been  supersaturated  at  the  lower 
temperature.  Any  disturbance  is  liable  to  produce  the 
crystallization. 


56 


WATER  AND  SOLUTION 


FIG.  26. —  CRYSTALLIZATION  OF  A  SUPERSATURATED  SOLUTION. 

a,  clear  supersaturated  solution;  b,  introduction  of  a  particle  of  the  solute; 

c,  crystallization  beginning;  d.  crystallization  complete. 


EFFLORESCENCE  AND  DELIQUESCENCE          57 

58.  Crystals.  —  The  fact  that  the  solubility  varies  with 
the  temperature  is  made  use  of  in  separating  solids  from 
solution.     If  a  solution  that  is  saturated  at  a  high  tem- 
perature be  allowed  to  cool  slowly,  the  dissolved  substance 
will   often   separate    into   definite    forms  called  crystals. 
Crystals  (Fig.  27)  are  symmetrical  and  often  transparent. 
Crystals  may  be  obtained  from  the  dilute  solution  of  a 
solid  by  the  evaporation  of  the  solvent. 

59.  Water  of  Crystallization Many  substances  in  crys- 
tallizing  from   aqueous   solutions   unite   with   a  definite 
quantity  of  water  which  is  necessary  to  the  shape  of  the 
crystal.     This    water   is    called  water   of  crystallization. 
Copper  sulphate  or  blue  vitriol  contains  water  of  crystal- 
lization, and  if  it  is  heated  in  a  test  tube,  moisture  will  be 
seen  on  the  cooler  portions  of  the  tube,  and  the  blue  crystal 
will  change  to  a  white  powder.     The  heating  has  driven 
off  the  water  of  crystallization. 

Substances  like  blue  vitriol  and  crystallized  zinc  sul- 
phate, formed  by  the  union  of  a  chemical  compound  with 
a  definite  amount  of  water,  are  often  termed  hydrates. 

60.  Efflorescence    and    Deliquescence.  —  If  a   crystal   of 
washing  soda  is  exposed  to  the  air  in  a  dry  place,  it  will 
lose  its  water  of  crystallization  and  become  covered  with 
a  fine  powder.     Such  a  material  is  said  to  be  efflorescent. 
An  efflorescent  substance  is  one  that  loses  water  of  crys- 
tallization on  exposure  to  the  air. 

Many  materials,  as  lime,  calcium  chloride,  and  caustic 
potash,  usually  absorb  moisture  from  the  air  and  are  there- 
fore said  to  be  hygroscopic.  If  they  absorb  sufficient  mois- 
ture to  dissolve  them  or  to  cause  them  to  become  wet,  they 
are  said  to  be  deliquescent.  Such  materials  are  useful  as 
drying  agents.  Whether  a  substance  will  give  up  its 


58 


WATER   AND   SOLUTION 


FIG.  27. —  CRYSTALS  OF  FAMILIAR  SUBSTANCES. 

a,  quartz  (ideal) ;  b,  quartz  (actual) ;  c,  galena  or  lead  sulphide  ;  d,  garnet 

e,  alum. 


HYDROGEN  PEROXIDE  59 

moisture  to  the  air  or  will  absorb  moisture  depends  largely 
on  the  amount  of  moisture  already  in  the  air  and  also  on 
the  temperature.  A  hygroscopic  substance  is  one  that 
will  absorb  moisture  from  the  air.  A  deliquescent  sub- 
stance is  one  that  absorbs  enough  to  become  wet. 

HYDROGEN  PEROXIDE 

Hydrogen  and  oxygen  form  a  compound  other  than 
water  in  which  the  weights  of  hydrogen  and  oxygen  are 
as  1  to  16.  As  it  contains  more  oxygen  for  a  given 
amount  of  hydrogen  than  water,  it  is  called  hydrogen 
peroxide  or  hydrogen  dioxide. 

61.  Preparation. —  Hydrogen  peroxide   is   prepared   by 
the  action  of  barium  peroxide  with  dilute  acids.     Com- 
mercially, the  barium  peroxide  is  mixed  with  water  to  the 
consistency  of  cream.     This  mixture  is  then  added  to  a 
dilute  solution  of  sulphuric  and  phosphoric  acids,  care  being 
taken  to  keep  the  temperature  below  15°  C. : 

barium  barium  hydrogen 

. ,     +    sulphuric  acid    — *-      .  ,  f, 

peroxide  sulphate          peroxide 

The  precipitate  of  barium  sulphate  and  phosphate  is 
allowed  to  settle  and  the  solution  of  hydrogen  peroxide 
decanted,  or  drawn  off. 

The  commercial  form  of  hydrogen  peroxide  is  its  3% 
solution.  To  prevent  the  peroxide  from  decomposition, 
the  solution  is  kept  slightly  acid  or  a  very  small  quantity 
of  acetanilid  is  sometimes  added.  It  is  sold  under  various 
trade  names,  such  as  "  Dioxogen  "  and  "  Aerozone." 

62.  Properties.  —  Hydrogen  peroxide  itself  is   a   clear, 
syrupy  liquid  about  1|  times  as  dense  as  water,  with  which  it 


60  WATER  AND  SOLUTION 

is  miscible.  Pure  hydrogen  peroxide  decomposes  with 
explosive  violence.  Even  in  the  dilute  3  %  water  solu- 
tion, the  decomposition  proceeds  slowly  according  to  the 
equation : 

hydrogen  peroxide    — >•    water    +    nascent  oxygen 

Nascent  oxygen  is  oxygen  at  the  moment  of  its  liberation 
from  a  compound. 

63.  Uses.  —  Upon  the  activity  of   the  nascent  oxygen 
depend  the  uses  of  "  peroxide "  as  a  bleaching  and  dis- 
infecting  agent.     Wool,  silk,   feathers,  hair,    and   ivory 
are  bleached  by  the  oxidation  of  their  coloring  matters. 
Harmful  bacteria  and  decomposing  matter  are  destroyed 
by  it ;  hence  its  use  as  an  antiseptic  for  superficial  wounds 
and  sores.     It  has  very  little  action  on  living  tissue,  and 
the  water  formed  in  its  decomposition  does  not  give  rise 
to  further  irritation,  as  many  other  disinfectants  do.     If 
acid  is  present,  this  may  cause  irritation.     For  this  reason, 
it  should  be  mixed  with  limewater  when  used  as  a  gargle. 

64.  Law  of  Multiple  Proportions. — In  water  the  weights 
of  the  hydrogen  and   oxygen  are   in  the  ratio  of   1  to 
8.      In  hydrogen   peroxide  the  ratio  is  1  to  16.      Thus 
the  hydrogen  in  the  peroxide  is  combined  with  twice  as 
much  oxygen  as  the  hydrogen  of  the  water.     A  similar 
relation  is  found  in  many  cases.     Whenever  two  substances, 
A  and  B,  unite  to  form  more  than  one  compound,  if  we  con- 
sider^  a  fixed  weight  of  A,  the  weights  of  B  which  combine 
with  this  fixed  weight  stand  in  simple  multiple  relation  to 
one   another.     These   ratios  may  be  expressed   by  small 
whole   numbers.     This  is  known  as  the  law  of  multiple 
proportions  or  Dalton's  second  law.     It  is  a  general  state- 
ment of  the  fact  that  we  observed  (§  46)  when  we  found 


SUMMARY  61 

that,  if  an  element  has  more  than  one  reacting  weight, 
these  weights  are  in  a  multiple  relation. 


SUMMARY 

Water  is  the  standard  for  specific  gravity  and  for  the  specific 
heat  of  liquids  and  solids.  Its  freezing  point  and  its  boiling  point 
are  respectively  0°  and  100°  on  the  Centigrade  thermometer. 

Water  can  be  purified  by  filtration,  distillation,  and  freezing. 

A  solution  is  a  uniform  mixture  that  does  not  conform  to  the  law 
of  definite  proportions. 

Water  is  the  most  common  solvent.  The  amount  of  a  solute  in 
a  given  quantity  of  a  solvent  causes  a  solution  to  be  either  unsatu- 
rated,  saturated,  or  supersaturated.  Important  temperature  changes 
take  place  during  solution. 

A  hygroscopic  substance  is  one  that  will  absorb  moisture  from 
the  air.  If  the  substance  absorbs  enough  moisture  to  become  wet, 
it  is  said  to  be  deliquescent. 

An  efflorescent  substance  is  one  that  loses  water  of  crystalliza- 
tion on  exposure  to  the  air.  "» 

Water  of  crystallization  is  the  definite  amount  of  water  with 
which  some  substances  combine  when  they  separate  from  a  solution 
as  crystals. 

Hydrogen  peroxide  can  be  prepared  by  the  addition  of  barium 
peroxide  to  cold  dilute  acids,  as  phosphoric,  sulphuric,  or  hydro- 
chloric. Hydrogen  peroxide  is  a  strong  oxidizing  agent  and  is  used 
as  a  germicide  and  for  bleaching. 

Hydrogen  peroxide  consists  of  1  part  by  weight  of  hydrogen 
combined  with  1 6  parts  by  weight  of  oxygen. 

The  composition  of  water  and  of  hydrogen  dioxide  illustrate  the 
law  of  multiple  proportions,  which  is :  Whenever  two  substances, 
A  and  B,  unite  to  form  more  than  one  compound,  if  we  consider 


62  WATER  AND   SOLUTION 

a  fixed  weight  of  A,  the  weights  of  B  which  combine  with  this  fixed 
weight  stand  in  simple  multiple  relation  to  one  another. 


EXERCISES 

1.  What  physical  properties  of  water  determine  the  fixed 
points  on  a  Centigrade  thermometer?  J 

2.  Why  does  water  put  out  fire  ? 

3.  How  can  salt  water  be  made  fit  for  drinking  ?  A 

4.  How  dees  a  solution  differ  from  a  chemical  compound  ? 

5.  What  is  the  chemical  statement  of  the  old  saying :  "  Oil 
and  water  will  not  ini&,"  ? 

6.  Distinguish  between  solvent/and  solute. 


7.  JWater  is  saturated  with  soda  at  a  high  temperature  and 


the  solution  is  allowed  to  cool.     Would  the  solution  then  be 
saturated  ?       '  ^(m^^.  . 

8.  How  could  you  determine  whether  a  certain  solution  is 
saturated,  unsaturated,  or  supersaturated  ?^//.  i/'/W  /ft****-  '  • 

9.  How   could  a  supersaturated  solution  /of  '/<  hypo  "  be 
prepared  ?    /dy 

10.  When  sea  water  is  evaporated,  why  does  one  of  the 
substances  in  solution  begin  to  separate  before  the  others  ? 

11.  How  would  you  show  that  any  natural  water  is  a  dilute 
solution.  ?/&/  W&dtf 


12.  Is  ammonia  more  soluble  in  cold  or  in  hot  water  ? 

&••      At  ;*L  • 

13.  Why  does  the  water  from  a  soda  fountain  bubble  so 

freely?  /l^^^^ 

14.  Why  are  salt  and  ice  used  in  ice  cream  freezers  ?   -1 
'£&(/ 

15.J  How  could  you  obtain  crystals  of  washing  soda  from 

the  dry  powder  ?    J&y 

16.   Distinguish  between  a  hygroscopic  and  a  deliquescent 
substance.     Give  an  example  of  each. 

'  •"  *-  >  ^; 


EXERCISES  63 

17.  Why  do  crystals  of  washing  soda  become  covered  with 

a  coating  of  white  powder  when  exposed  to  the  air  ?   ' 
MrMJw  0f  QAWsT  t -.-  :^-^-^n^ 

18.  Way  .is  fused  calcium  chloride  used  as  a  drying  agent  ? 

19.  There  are  five  oxides  of  nitrogen  in  which  the  weights 
of  oxygen  and  nitrogen  are  respectively  in  the  ratios :  16 : 28, 
32  :  28,  48 :  28,  64  :  28,  and  80 :  28.     Show  how  the  composition 
of  these  compounds  illustrates  the  law  of  multiple  proportions. 

"  20.   JV£en£ion  three  ways  by  which  water  can  be  purified. 

21.  How  does  the  composition  of  water  illustrate  the  law  of 
definite  proportions  ? 

*Sr**t<f      --  //r~2-'JL''>c-' 

22.  Why  does  not  a  solution  of  hydrogen  peroxide  keep 

well  when  open  to  the  air  ? 

23.  If  sold  at  the  same  price  per  pound,  would  it  be  more 
economical  to  buy  washing  soda  before  or  after  it  has  been  ex- 
posed to  the  air  for  some  time  ? 


CHAPTER  VII 
ATOMS  AND  MOLECULES 

65.  Law  of  Conservation  of  Mass.  —  We   have    studied 
several  substances  and  some  of  the  laws  governing  the 
quantities  of  matter  that  take  part  in  chemical  actions, 
without  attempting  any  description  of   the  structure  or 
make-up  of  the  materials  used. 

Matter  is  generally  defined  as  anything  that  takes  up 
room.  The  different  kinds  of  matter  are  called  substances. 
So  far  as  we  know,  matter  is  indestructible,  nor  has  any  one 
succeeded  in  making  something  from  nothing.  We  may 
change  its  properties,  but  we  always  have  the  same  amount 
of  matter  after  the  change  as  before. 

A  concise  statement  of  these  facts  is  embodied  in  the 
law  of  the  conservation  of  mass,  which  may  be  stated  as 
follows  :  The  total  mass  of  matter  taking  part  in  any  chemi- 
cal process  remains  unchanged. 

66.  Atomic  Hypothesis.  —  We  found  that  the  combining 
or  reacting  weights  are  different  for  various  elements  but 
are  constant  or  unchanging  for  each  element.     There  is 
apparently  something  significant  in  the  fact  that  in  the 
compounds  of  oxygen  with  hydrogen  the  amount  of  oxygen 
combined  with  a  given  weight  of  hydrogen  is  eight,  or 
twice  eight,  times  the  weight  of  the  hydrogen. 

Since  water  is  composed  of  eight  parts  of  oxygen  and  one 
part  of  hydrogen,  the  smallest  masses  of  water  must  have 
this  composition.  For  the  same  reason,  the  smallest 

64 


MOLECULES  65 

masses  of  hydrogen  peroxide  must  contain  sixteen  parts 
of  oxygen  to  one  of  hydrogen.  There  must  be  some 
reason  why  this  number  eight  is  characteristic  of  oxygen, 
and  why  there  is  no  compound  of  these  elements  in  which 
the  ratio  is  twelve  to  one  or  twenty  to  one. 

John  Dalton  in  1805  made  certain  assumptions,  known 
as  the  atomic  hypothesis,  by  which  we  can  readily  explain 
these  facts.  These  assumptions  were  : 

1st,  matter  is  made  up  of  small  particles  called  atoms ; 

2d,  atoms  possess  the  power  of  attracting  or  holding  on 
to  other  atoms; 

3d,  atoms  do  not  subdivide  in  taking  part  in  chemical 
changes ;' 

4th,  one  atom  of  an  element  is  exactly  like  every  other 
atom  of  that  element  but  differs  from  an  atom  of  any 
other  element. 

67.  Atoms.  —  An  atom  is  the  smallest  particle  of  an  ele- 
ment that  takes  part  in  a  chemical  change.     Different 
kinds   of  atoms   differ  in  weight,  form,  and  combining 
power,  but  all  atoms  of  the  same  element  must  be  alike. 
All  the  atoms  of  hydrogen  are  alike ;   all  the  atoms  of 
oxygen  are  alike. 

68.  Molecules.  —  We  found  that  when  oxygen  and  hy- 
drogen combined,  a  substance  was  formed  which  possessed 
properties  differing  from  either  of  these  elements.     The 
smallest  conceivable  quantity  of  water  will  possess  the 
same  characteristic  properties  as  any  amount  that  we  can* 
directly  observe.      The  smallest  quantity  of  a  substance 
having  the  properties  of  the  mass  is  called  a  molecule. 
We  may  assume  that  each  atom  of  oxygen  is  accompanied 
by  an  atom  of  hydrogen  that  always  holds  on  to  it.     The 
mass  made  up  of  such  a  pair'of  minute  particles  does  not 


66  ATOMS  AND  MOLECULES 

have  the  properties  of  hydrogen  or  of  oxygen.  It  is  a 
new  substance — an  oxide  of  hydrogen.  Molecules  are 
usually  aggregations  of  atoms.  The  molecule  is  the 
physical  unit  of  the  mass,  as  the  atoms  comprising  it  do 
not  separate  during  physical  changes. 

69.  Explanation  of  the  Law  of  Definite  Proportions.  —  Ac- 
cording to  the  atomic  hypothesis,  each  molecule  of  water 
consists  of  a  definite  number  of  atoms  of  hydrogen  in  com- 
bination with  a  definite  number  of  atoms  of  oxygen. 
Since  every  atom  of  the  same  element  has  the  same 
weight,  the  molecule  of  water  must  have  a  definite  per- 
centage composition.  ^f 

Let  us  assume  the  mass  of  the  oxygen  atom  to  be  8 
times  that  of  the  hydrogen  atom,  and  the  molecule  of 
water  to  be  composed  of  1  atom  of  oxygen  in  combination 
with  1  atom  of  hydrogen.  Then  the  water  molecule 
would  contain  8  parts  by  weight  of  oxygen  and  1  part  by 
weight  of  hydrogen,  or  88.89%  of  oxygen  and  11.11%  of 
hydrogen.  Now  a  large  quantity  of  water  is  merely  a  very 
great  number  of  molecules  and  therefore  must  have  the 
same  percentage  composition  as  the  single  molecule  of 
water.  This  would  explain  why  it  is  impossible  to  make 
8.3  grams  of  oxygen  unite  with  1  gram  of  hydrogen. 
These  weights  do  not  contain  equal  numbers  of  atoms ; 
the  mass  of  the  oxygen  will  contain  the  larger  number. 
Consequently,  when  combination  takes  place,  a  number  of 
oxygen  atoms  would  remain  unused.  The  mass  of  oxy- 
gen that  has  combined  would  weigh  exactly  eight  times 
as  much  as  the  hydrogen.  The  0.3  gram  excess  of  oxy- 
gen would  remain  uncombined. 

Whatever  the  weight  of  the  atoms  may  be,  chemical 
action  must  take  place  between  definite  masses  of  sub- 
stances, and  the  composition  of  a  compound  must  be 


RELATION  OF  REACTING  TO  ATOMIC   WEIGHTS    67 

definite.  The  law  of  definite  proportions,  which  states 
that  the  percentage  composition  of  a  chemical  compound 
is  constant,  is  explained  by  assuming  that  chemical  com- 
binations always  take  place  between  atoms. 

70.  Explanation  of    the  Law    of  Multiple  Proportions. — 

The  law  of  multiple  proportions  states  that  whenever  two 
substances,  A  and  B,  unite  to  form  more  than  one  chemi- 
cal compound,  the  weights  of  B  that  unite  with  the  fixed 
weight  of  A  are  in  the  ratio  of  small  whole  numbers. 
Now,  a  fixed  weight  of  A  is  equivalent  to  a  definite  num- 
ber of  atoms  of  an  element.  If  the  hydrogen  oxide  mole- 
cule is  composed  of  one  atom  of  hydrogen  and  one  atom 
of  oxygen,  we  can  imagine  combinations  of  one  atom  of 
hydrogen  with  two,  three,  or  more  oxygen  atoms.  What- 
ever the  combination  may  be,  it  is  evident  from  the  atomic 
hypothesis  that  the  weight  of  oxygen  combined  with  a 
certain  quantity  of  hydrogen  must  be  an  integral  multiple 
of  the  amount  which  combines  with  the  hydrogen  to  form 
hydrogen  oxide. 

71.  Relation  of  Reacting  to  Atomic  Weights.  — The  react- 
ing weights  are  ratios  between  the  weights  of  different 
kinds  of  atoms,  or  multiples  of   these  weights.      If  we 
knew  that  in  water  one  atom  of  oxygen  was  combined 
with  one  atom  of  hydrogen,  as  we  assumed,  the  weight  of 
the  oxygen  atom  would  be  eight  times  that  of  the  hydro- 
gen atom.     If,  however,  there  are  two  atoms  of  hydrogen 
to  each  oxygen  atom,  the  one  atom  of  oxygen  must  weigh 
sixteen  times  as  much  as  one  atom  of  hydrogen.     If  there 
are  two  oxygen  atoms  to  each  hydrogen  atom,  each  oxygen 
atom  would  be  four  times  as  heavy  as  the  one  hydrogen 
atom. 

If  we  know  how  many  of  each  kind  of  atom  there  are 


68  ATOMS  AND  MOLECULES 

in  a  molecule,  we  can  find  the  relative  weights  of  the 
atoms.  Such  determinations  have  been  made  by  com- 
parison of  physical  properties. 

72.  Value  of  Atomic  Hypothesis.  —  The  atomic  hypothesis 
gives  a  convenient  way  of  explaining  the  facts  upon 
which  the  laws  of  definite  and  multiple  proportions  are 
based.  We  must  not  forget,  however,  that  the  laws  are 
statements  of  facts,  based  on  experimental  evidence,  while 
the  atomic  hypothesis  is  used  in  the  attempt  to  picture  a 
structure  or  process  which  would  agree  with  the  facts. 
We  do  not  know  that  this  is  the  way  that  matter  is  made 
up.  Perhaps  in  time  a  better  explanation,  based  on  dif- 
ferent suppositions,  may  be  offered,  but  we  do  know 
that  it  has  proved  useful  in  explaining  a  wide  variety  of 
facts  and  has  done  more  than  any  other  theory  for  the  ad- 
vancement of  chemistry.  Practically  all  scientific  explana- 
tions of  chemical  phenomena  are  based  on  this  hypothesis. 


SUMMARY 
Matter  is  anything  that  takes  up  room. 

Law  of  Conservation  of  Mass.  — •  Matter  is  indestructible.  Its 
properties  may  be  changed,  but  there  is  always  the  same  amount 
of  matter  after  a  change  as  before. 

The  study  of  the  weight  relations  of  chemical  changes  shows 
that  each  element  has  its  definite  combining  or  reacting  weight. 
The  amount  of  any  element  found  in  chemical  compounds  is 
either  this  reacting  weight  or  some  multiple  of  it. 

These  facts  are  explained  by  the  atomic  hypothesis.  This  as- 
sumes matter  to  be  made  up  of  small  particles  which  attract  or 
hold  on  to  other  particles,  but  which  do  not  subdivide  in  chemical 
changes. 


EXERCISES  69 

Atoms  are  the  smallest  particles  of  an  element  that  take  part 
in  chemical  changes.  All  the  atoms  of  an  element  are  alike  and 
possess  the  characteristic  properties  of  that  element,  but  differ 
from  the  atoms  of  all  other  elements.  A  molecule  is  the  smallest 
quantity  of  a  substance  having  the  properties  of  the  mass. 

The  atomic  hypothesis  gives  a  convenient  explanation  of  the 
facts  upon  which  the  laws  of  definite  and  multiple  proportions  are 
based.  It  has  been  the  most  valuable  theory  in  the  establishment 
of  chemistry  as  a  science.  Sometime  a  better  explanation  may 
replace  this  hypothesis. 

EXERCISES 

1.  Why  was  an  extended  study  of  the  composition  of  sub- 
stances necessary  before  the  atomic  hypothesis  could  be/eason- 
a^accepted?  ^ 

y  "2.  Mercury  is  put  into  a  glass  'fla£k  which  is  then  sealed, 
weighed,  heated,  and  weighed  again.  Why  is  there  no  change 
in  the  weight,  although  the  mercury  turns  to  a  red  powder  ?  , 

3.  Why  is   it   that   the   attempt   to   make  35.5  grams  of 
chlorine  combine  with  24  grams  of  sodium,  always  leaves  1 
grain  of  sodium  uncombined  ?  ^dtd-^i  £ 

4.  Dalton  knew  that  one  oxide  of  carbon  contained  2|  parts 
of  oxygen  to  1  part  of  carbon  and  that  another  oxide  was  com- 
posed of  1^  parts  of  oxygen  to  1  part  of  carbon.     What  law  do 
these  two  facts  illustrate?     Explain  them  according  to  the 
atomic  hypothesis. 

5.  Sulphur  dioxide  contains  50  %  of  sulphur  and  50  %  of 
oxygen.     Sulphur  trioxide  contains  40  %  of  sulphur  and  60  % 
of  oxygen.     Show  how  these  facts  can  be  used  to  illustrate  the 
law  of  Multiple  Proportions. 

6.  Why  is  the  molecule  of  more  importance  in  physics  than 
in  chemistry  ?  /&, 

7.  Why  was  not  tfie  present  atomic  hypothesis  evolved  be- 
fore  the  time  of  Lavoisier  ?  {^j^t^OU/* 


70  ATOMS  AND  MOLECULES 

8.  Dalton  showed  that  for  one  part  by  weight  of  hydrogen 
olefiant  gas  contained  twice  as  many  parts  by  weight  of  car- 
bon as  marsh  gas.     Explain  these  facts  according  to  the  atomic 
hypothesis. 

/W  ,-•   f  AyJdV'    -^  vt^'u^x^  **$-  '-  ' 

9.  Explain  this  statement:  "Without  the  atomic  concep- 
tion, chemistry  would  be  a  chaos  of  unrelated  facts ;  with  the 
theory,  it  has  become ^n  orderly  science"  (T.  W.  Clarke) f' 

10.  State  the  four  assumptions  of  the  atomic  hypothesis  of 
Dalton. 

11.  Show  how  the  decomposition  of  the  red  oxide  of  mercury 
illustrates  the  law  of  conservation  of  mass. 

12.  Why  is  a  knowledge  of  reacting  weights  valuable  in  the 
manufacture  of  synthetic  compounds  ? 

,.^vt'U,cA     fit     &tek        j^i     .->;<    • 

; 

'    ,/vr 


CHAPTER   VIII 
££  CHLORINE      I 

73.  Chlorine  may  be  said  to  be  a  typical  non -metallic 
element.     It  displays  in  a  marked  degree  those  properties 
which  are  regarded  as  characteristic  of  the  non-metals. 
The  most  abundant  compound  of  chlorine  found  in  nature 
.is  sodium  chloride,  common  salt.     Sodium  chloride  is  a 
very  stable  compound ;  heat  does  not  decompose  it  except 
at  an  extremely  high  temperature.     Chlorine  can  be  ob- 
tained from  it  in  several  ways. 

74.  Preparation   by   Electrolysis.  —  An   electric   current 
can  be  passed  through  a  solution  of  common  salt,  using 
apparatus  similar  to  that  used  in  the  electrolysis  of  water. 
The  electrodes  in  this  case,  however,  should  be  of  carbon, 
since  platinum  slowly  combines  with  the  chlorine  that  is 
evolved.     The  apparatus  is  filled  with  a  concentrated  solu- 
tion of  salt.     When  the  current  passes,  chlorine  is  evolved 
as  a  gas  at  the  anode  and  hydrogen  at  the  cathode.    Sodium 
is  probably  first  liberated  at  the  cathode ;    but  since  this 
element  reacts  rapidly  with  water,  it  is  impossible  for  it 
to  accumulate.     Hydrogen  is  set  free  as  a  result  of  the 
action  of  sodium  with  water. 

sodium  chloride  — *-  sodium  +  chlorine  "^ 
sodium  +  water  — >-  hydrogen  +  sodium  hydroxide 

:-  fSk.     Tv/4  ,  0    ->'•#,      f  a  VU.  0  £ .' 
As  the  final  products,  we  have  the  two  gases,  hydrogen 

and  chlorine,  and  sodium  hydroxide  which  is  dissolved  in 
the  water. 

'    - 


72 


CHLORINE 


75.    Preparation    by    Oxidation    of    Hydrochloric    Acid. — 

Hydrochloric  acid  is  a  solution  of  a  compound  of  hydro- 
gen and  chlorine.  The  chlorine  might  be  separated  by 
electrolysis,  but  it  is  more  usual  to  take  advantage  of  the 
fact  that  hydrogen  has  a  great  tendency  to  combine  with 
oxygen;  so  that  if  we  oxidize  hydrochloric  acid,  the 
hydrogen  will  combine  with  the  oxygen  to  form  water, 
and  free  chlorine  will  be  obtained.  Oxygen  from  the 
air  may  be  used.  Hydrogen  chloride  (gas)  and  air  are 
passed  through  a  heated  tube  containing  a  catalytic  agent 

(copper  chloride).  The 
action  is  slow  and  can 
be  well  carried  out  only 
on  a  large  scale. 

Often  on  a  commer- 
cial  scale,  and   in   the 
laboratory,    manganese  4 '.-. 
dioxide  is  the  oxidizing 
agent  employed.     Con- 
FIG.  28 .  — PREPARATION  OF  CHLORINE.         centrated    hydrochloric 
a,  generating  flask;   b,  bottles  for  collec-     acid    solution  is  mixed 
tion  of  gas ;  c.  pan  of  warm  water.  ^       manganege       di_ 

oxide ;  when  the  mixture  is  warmed,  chlorine  is  evolved 
(Fig.  28).  The  hydrogen  of  the  acid  combines  with 
the  oxygen  of  the  dioxide,  forming  water.  The  man- 
ganese combines  with  half  the  chlorine  of  the  acid, 
forming  manganese  chloride,  which  dissolves  in  the  water 
the  remaining  portion  of  the  chlorine  is  evolved  as  a  gas: 

...    ,   ALlt     .,  t    Hfr*       <?l~ 

(^hydrochloric  acid  +  manganese  dioxide  — >• 
water  -f-  manganese  chloride  +  chlorine 

.  o- .  tL.  04  /vta  •       C£-  <is  -f    UL-  ty' 

The  chlorine  isrnot  'usually  collected  over  water,  since 
dry  chlorine  is  desirable  for  many  experiments  and  since 
water  dissolves  twice  its  own  volume  of  chlorine  at  ordinary 


ACTION   WITH  METALS  73 

temperatures.  It  is  commonly  collected  by  displacement 
of  air,  or  over  salt  water,  in  which  it  is  scarcely  soluble. 
Its  density  and  color  render  its  collection  by  downward 
displacement  a  simple  matter. 

A  mixture  of  salt,  sulphuric  acid,  and  manganese  dioxide 
is  often  used.  The  salt  and  sulphuric  acid  react  and  form 
hydrochloric  acid,  which  is  then  oxidized  by  the  manga- 
nese dioxide. 

76.  Physical  Properties. —  Chlorine  is  a  greenish  yellow 
gas,  nearly  2^  times  as  dense  as  air ;  it  dissolves  somewhat 
in  water. 

Chlorine  has  an  intensely  disagreeable  odor,  and  attacks 
the  membrane  of  the  nasal  passages  and  lungs,  producing 
effects  something  like  those  of  a  bad  cold.  It  is  very 
poisonous ;  a  full  breath  of  the  pure  gas  would  probably 
cause  death.  Inhaling  weak  ammonia  or  alcohol  will 
'counteract  some  of  the  effects.  Chlorine  should  be  pre- 
pared and  handled  with  caution  to  prevent  any  possibility 
of  inhaling  it. 

CHEMICAL  PROPERTIES 

77.  Action    with    Metals.  —  Chlorine    is    a    very    active 
element.     It  combines  directly  with  many  other  elements, 
especially   metals,   forming   chlorides.      When   powdered 
antimony  is  sprinkled  into   a   jar   of   chlorine,  brilliant 
sparks  are  seen  and  a  white  cloud  of  antimony  chloride 
is  produced.     Arsenic,  zinc,  copper,  and  iron,  especially 
when  heated,  also  unite  readily  with  chlorine,  with  the 
formation  of  chlorides : 

</  //N,  -  •  >-~{ib*  »v>  —>  //f^'Y*"-"***  &•* •'• 

antimony  +  chlorine  — >•  antimony  chloride 
arsenic      4-  chlorine  — >•  arsenic  chloride 
iron  +  chlorine  — >-  iron  chloride 

zinc  +  chlorine  — >-  zinc  chloride 


74  CHLORINE 

These  are  true  cases  of  combustion,  since  heat  and  light 
appear.  So  we  may  say  chlorine  supports  combustion,  and 
thus  resembles  oxygen. 

When  molten  sodium  comes  in  contact  with  chlorine,  it 
blazes  with  a  dazzling  light,  sodium  chloride  (common  salt) 
being  formed.  To  one  who  for  the  first  time  observes  the 
change,  it  seems  almost  incredible  that  a  harmless,  house- 
hold necessity  like  common  salt  could  result  from  the 
union  of  a  gas  possessing  the  disagreeable  and  poisonous 
properties  of  chlorine,  with  a  metal  that  has  sufficient 
energy  to  decompose  water. 

78.  Action  with  Hydrogen.  —  If  a  jet  of  hydrogen  is 
ignited  in  the  air  and  lowered  into  a  jar  of  chlorine,  a 
pale,  nearly  white  flame  will  be  produced;  the  color  of 
the  chlorine  will  disappear,  and  in  the  jar  we  will  find  a 
colorless  gas,  hydrogen  chloride,  which  fumes  strongly  in 
moist  air.  Much  heat  is  given  off  in  the  union  of  chlorine 
with  hydrogen  —  another  similarity  between  the  behavior 
of  chlorine  and  oxygen.  A  mixture  of  chlorine  and 
hydrogen  will  not  combine  in  the  dark ;  in  diffused  day- 
light they  combine  slowly,  and  explode  when  exposed  to 
direct  sunlight  or  other  bright  light. 

The  great  tendency  of  chlorine  to  combine  with  hydro- 
gen is  shown  by  the  fact  that  it  will  abstract  hydrogen 
from  many  compounds.  Turpentine  is  a  compound  of 
carbon  and  hydrogen.  If  a  piece  of  paper  is  moistened 
with  warm  turpentine  and  thrown  into  a  jar  of  chlorine,  a 
violent  action  occurs,  often  with  the  production  of  a  flame, 
and  a  heavy  deposit  of  soot  (carbon)  forms  on  the  side  of 
the.  bottle.  If  the  breath  is  blown  into  the  bottle,  the 
moisture  will  cause  the  hydrogen  chloride  there  to  fume. 
An  action  similar  to  that  with  the  turpentine  is  seen  in 
the  burning  of  a  wax  taper  in  chlorine.  Paraffin  wax, 


ACTION   WITH   WATER  75 

like  turpentine,  contains  carbon  combined  with  hydrogen, 
and  only  the  latter  unites  with  the  chlorine. 

79.  Action  with  Water.  —  Although  water  is  a  very  stable 
substance,  under  certain  circumstances  chlorine  will 

react  with  it,  combining  with  the  hydrogen  to  form 
hydrochloric  acid  and  setting  the  oxygen  free. 
If  a  tube  is  filled  with  a  solution  of  chlorine  in 
water  and  is  allowed  to  stand  in  the  sunlight, 
oxygen  is  slowly  formed  and  collects  at  the  top 
of  the  tube  (Fig  29): 

water  -f-  chlorine  — >-  oxygen  4-  hydrochloric  acid 

'  C/  L  £-  i-  $•  Jb.Ji  - 

The  acid  formed  is  dissolved  by  the  water. 
Chemical  actions  brought  about  by  the  action  of 
light  are  not  uncommon;  an  important  example 
is  the  formation  of  starch  in  the  green  leaves  of 
plants  under  the  influence  of  sunlight.  Photo- 
graphic processes  also  depend  on  the  effect  of 
light  on  chemical  action. 

Chlorine  is  able  to  decompose  water  in  the 
absence  of  light,  provided  there  is  present  an 
oxidizable  substance.  For  this  reason  chlorine 
water  is  a  good  oxidizing  agent;  the  chlorine 
combines  with  the  hydrogen  of  the  water,  and  the 
oxygen  set  free  combines  with  the  other  material 
present.  FIG.  29. 

USES 

80.  Bleaching.  —  The  chief  commercial  use  of  chlorine  is 
as  a  bleaching  agent,  especially  for  cotton  goods.     Cotton 
fiber  is  not  naturally  white.     If   unbleached   or  colored 
goods  are  placed  in  a  jar  of  chlorine,  no  action  takes  place 
if  the  cloth  is  dry ;  but  if  moist,  many  colors  are  quickly 


76 


CHLORINE 


destroyed  (Fig.  30).  Some  colors  are  not  bleached  by 
chlorine.  Many  dyes  and  the  coloring-matter  of  many 
fibers  are  easily  oxidizable  materials;  so  that  when  the 
chlorine  acts  with  the  water,  forming  hydrochloric  acid, 
the  oxygen  set  free  changes  the  coloring-matter  to  colorless 
compounds.  Chlorine,  will  bleach  some  colored  com- 
pounds by  decomposing  them  and  combining  with  the 


f~ 


FIG.  30.  —  BLEACHING  WITH  CHLORINE. 

a,  dry  colored  cloth ;  b,  wet  cloth ;  c,  c,  calcium  chloride  to  keep  moisture 
from  dry  cloth. 

hydrogen  of  the  dye.     Chlorine  cannot  be  used  to  bleach 
silk  and  wool,  as  it  attacks  these  fibers. 

Chlorine  is  produced  in  great  quantities  as  a  by-product 
of  sodium  hydroxide  manufacture  by  the  electrolysis  of 
brine.  It  is  sometimes  liquefied,  in  order  to  transport  it 
easily  for  use  at  a  distant  point.  In  bleaching,  however, 
chlorine  gas  is  not  so  generally  used  as  is  bleaching-pow- 
der,  a  compound  obtained  by  absorbing  chlorine  in  slaked 


USES 


77 


lime.  The  cotton  cloth  is  soaked  in  a  solution  of  this,  and 
then  in  dilute  acid  to  liberate  the  chlorine,  and,  finally, 
is  thoroughly  washed  to  remove  the  chemicals  (Fig.  31). 

In  the  bleaching  action,  the  destruction  of  the  color  was 
attributed  to  the  oxygen ;  but  oxygen  does  not  ordinarily 
bleach  even  weak  dyes.  It  is  found  that  in  general  ele- 
ments are  more  active,  that  is,  have  a  greater  tendency  to 
combine  with  other  substances,  if  the  elements  come  in 
contact  with  the  substances  at  the  moment  of  their  libera- 
tion from  a  compound.  An  element  acting  under  these 
conditions  is  said  to  act  in  the  nascent  (just  born)  state. 


FIG.  31.  —  DIAGRAMMATIC  REPRESENTATION  OF  BLEACHING. 

a,  cloth;  b,  b,  bleaching  powder  solutions ;  c,  c,  acid  solutions ;  d, "  anti-chlor  " 

(sodium  sulphite  solution)  ;  e,  water ;  /,  drying  rolls ;  g,  ironing  rolls. 

81.  Disinfecting.  —  Nascent  oxygen  will  readily  oxidize 
and  kill  microscopic  organisms,  such  as  disease  germs. 
Hence  chlorine,  which  sets  oxygen  free,  is  a  good  disin- 
fectant. Bleaching  powder  (chloride  of  lime)  affords  a 
convenient  source  of  chlorine  for  this  purpose ;  on  stand- 
ing exposed  to  air,  chlorine  is  slowly  given  off.  The  car- 
bon dioxide  of  the  air  unites  with  water  to  form  a  weak 
acid,  which  reacts  with  the  bleaching  powder,  liberating 
chlorine.  The  gas  can  be  rapidly  liberated  by  the  addi- 
tion of  any  common  acid  to  the  bleaching  powder.  Bleach- 
ing powder  is  one  of  the  cheapest  and  most  widely  used 
disinfectants.  In  recent  years,  this  and  other  compounds 
yielding  chlorine  have  come  into  extensive  use  for  freeing 
the  drinking  water  for  cities  and  towns  from  harmful  dis- 
ease germs  with  which  it  is  contaminated. 


78  CHLORINE 


SUMMARY 

Chlorine  occurs  in  nature  combined  with  metals,  the  most 
important  compound  being  salt. 

Chlorine  is  prepared :  ( 1 )  by  electrolysis  of  brine  ;  (2)  by  oxida- 
tion of  hydrochloric  acid ;  (3)  by  the  action  of  salt  with  a  mixture 
of  manganese  dioxide  and  sulphuric  acid.  The  first  and  last 
methods  are  the  more  common. 

Properties.  —  Atomic  weight,  35.5.  Density,  3.2  grams  per 
liter.  One  volume  of  water  at  ordinary  temperature  dissolves 
about  two  volumes  of  chlorine. 

Chlorine  is  a  greenish  yellow,  poisonous  gas  characterized  by  a 
pungent  odor  and  by  its  chemical  activity.  It  reacts  with  metals  to 
form  chlorides,  and  with  hydrogen  and  many  hydrogen  compounds 
to  form  hydrogen  chloride.  Its  reaction  with  water,  yielding 
nascent  oxygen,  is  utilized  in  bleaching  cotton  goods. 

The  principal  uses  of  chlorine  are  for  bleaching,  disinfecting,  ex- 
traction of  metals  from  ores,  and  the  purification  of  water. 

EXERCISES 

1.  Melted    sodium    chloride    on    being    electrolyzed    gives 
sodium  and  chlorine.     Why  does  not  the  solution  yield  the 
same  products  ? 

2.  In  the  mixture  of  salt,  sulphuric  acid,  and   manganese 
dioxide,  used  in  the  preparation  of  chlorine,  what  is  the  use  of 
each? 

3.  If  a  solution  of  chlorine  is  allowed  to  stand  in  the  sun- 
light, bubbles  collect  and  the   color   of  the   solution   fades. 
Why? 

4.  Cotton  cloth  soaked  for  a  long  time  in  chlorine  bleaching 
solution  falls  to  pieces.     Why  ? 

5.  Chlorine  injures  wool.    What  substance,  already  studied, 
is  used  to  bleach  wool  ? 


EXERCISES  79 

6.  Describe  a  case  of  combustion  in  which  oxygen  is  not 
involved. 

7.  Compare  chlorine  and  oxygen   with   respect  to  their 
chemical  activity. 

8.  When  chlorine  water  is  to  be  used  for  testing  purposes 
in  the  laboratory,  why  should  it  always  be  freshly  prepared  ? 

9.  Explain  the  action  of  chlorine  on  colored  cloth  when  wet. 

10.  State  the  methods  used  for  collecting  chlorine  gas  and 
explain  why  they  are  selected. 

11.  If  you  accidentally  inhaled  some  chlorine  in  the  labora- 
tory, what  means  would  you  employ  to  counteract  its  effects  ? 

12.  Why  are  earthenware  rather  than  metal  pipes  employed 
to  carry  chlorine  from  one  part  of  a  bleaching  powder  factory 
to  another  ? 

13.  Give  at   least  two  cases  in   which  light  produces  or 
hastens  chemical  action. 

14.  How  is  bleaching  powder  made  ?     State  and  explain  two 
uses  of  bleaching  powder. 

15.  What  is  meant  by  "  nascent  oxygen  "  ?     Name  two  sub- 
stances which  depend  on  nascent  oxygen  for  their  disinfecting 
action. 


CHAPTER   IX 

HYDROCHLORIC  ACID 

82.  Preparation.  —  One  of  the  most  important  com- 
pounds of  chlorine  is  hydrogen  chloride,  whose  water 
solution  is  hydrochloric  acid.  .  As  its  name  implies,  it 
may  be  made  by  the  direct  union  :of  hydrogen  and  chlo- 
rine, but  the  combination  is  so  violent  that  only  small 
quantities  can  be  made  at  a  time.  It  may  be  more  con- 
veniently prepared  by  taking  a  chloride,  e.g.  sodium  chlo- 
ride, and  adding  concentrated  sul- 
phuric acid  (Fig.  32).  The  action 
begins  immediately  and  the  gaseous 
hydrogen  chloride  is  evolved  so 
easily  that  little  heating  is  neces- 
sary. Too  violent  action  may  be 
avoided  by  the  successive  additions 
of  small  quantities  of  the  sulphuric 
acid  to  the  chloride,  using  a  pan  of 
hot  water  to  heat  the  mixture.  The 
action  may  be  represented  thus : 


FIG.  32. 


sodium  chloride  +  sulphuric  acid  — >. 

M^  sodium  (hydrogen     /> 

\chlorine  £<  sulphur 

^    [oxygen         J 

sodium  sulphate  ~h  hydrogen  chloride 

f  sodium  /  hydrogen 

<  sulphur  |  chlorine 

[oxygen 

80 


PHYSICAL   PROPERTIES  81 

The  chlorine  (of  the  salt  combines  with  the  hydrogen 
from  the  sulphuric  acid,  and  the  sodium  with  the  other 
part  of  the  sulphuric  acid,  that  is,  with  the  sulphur  and 
oxygen. 

The  hydrogen  chloride  gas  may  be  collected  by  the 
downward  displacement  of  the  air,  or,  better,  over  mer- 
cury, since  this  metal  is  not  attacked  by  the  gas.  More  fre- 
quently, however,  the  gas  is  dissolved  in  water,  forming 
hydrochloric  acid,  and  the  acid  solution  used.  ^^ 

83 .  General  Method  for  Preparing  Acids.  —  The  preparation  * ,? 
of  hydrochloric  acid  illustrates  a  general  method  for  pre-  •jfrtt 
paring  volatile  acids.     Sulphuric  acid  is  used  because  it 
boils    (vaporizes)   at  a  comparatively  high   temperature 
(338°  C.),  while  hydrochloric  acid  vaporizes  at  a  much 
lower  temperature.     When  the  sulphuric  acid  comes  in 
contact  with  a  chloride,  a  reaction  occurs  and  some  hydro- 
chloric acid  is  formed.     The  excess  of  sulphuric  acid,  the 
newly  formed  hydrogen  chloride  and  its  solution,  hydro- 
chloric acid,  are  then  present  in  the  mixture.     The  lower 
boiling   hydrochloric    acid,   however,   is    soon    vaporized, 
since  its  boiling  point  is  many  degrees  below  the  tempera- 
ture at. which  the  operation  is  conducted.     The  higher 
boiling    sulphuric    acid    remains    behind    and    gradually 
completes  its  reaction  with  the  sodium  chloride.     Finally, 

all  the  hydrochloric  acid  is  driven  off  and  any  excess  of 
sulphuric  acid  remains  mixed  with  the  sodium  sulphate. 
Sulphuric  acid  is  generally  used  in  the  preparation  of 
other  acids. 

84.  Physical  Properties.  —  Hydrogen  chloride  is  a  color- 
less gas  with  a  sharp,  penetrating  odor.     It  is  slightly 
heavier  than  air.     Its  solubility  in  water  is  most  striking, 
between  four  and  five  hundred  volumes  of  the  gas  dis- 
solving  in  one   volume  of   water  at  room  temperature. 


82  HYDROCHLORIC  ACID 

This  solution,  commonly  known  as  hydrochloric  acid  or 
muriatic  acid,  contains  about  38%  by  weight  of  the  hy- 
drogen chloride.  The  high  solubility  of  the  gas  causes  it 
to  unite  with  the  moisture  of  the  air,  condensation  occurs, 
and  the  minute  particles  of  the  resulting  liquid  appear  as 
a  white  mist  or  fumes,  which  can  be  seen  when  a  concen- 
trated solution  of  hydrochloric  acid  is  exposed  to  the  air. 
The  fuming  is  still  more  marked  when  the  moist  breath  is 
blown  across  the  mouth  of  a  tube  from  which  hydrogen 
chloride  gas  is  issuing. 

Hydrogen  chloride  can  be  liquefied  and  also  solidified 
at  low  temperatures  with  increased  pressure. 

85.  Chemical  Properties.  —  Neither  liquid  hydrogen  chlo- 
ride nor  the  gas,  when  perfectly  dry,  shows  the  chemical 
properties  characteristic  of  the  acids.     These  properties 
belong  to  the  water  solution.     Hydrochloric  acid,  then,  is 
the  aqueous  solution  of  hydrogen  chloride.     The  water 
solution  has  a  sour  taste,  changes  blue  litmus  to  red,  and 
reacts  with  many  metals,  setting  free  hydrogen  and  form- 
ing a  chloride  of  the  metal. 

There  are  four  common  metals  with  which  hydrochloric 
acid  does  not  react.  These  metals  are  exceptional  in  their 
action  with  acids  in  general.  They  are  mercury,  silver, 
copper,  and  lead.  Zinc  and  iron  are  typical  of  the  metals 
with  which  hydrochloric  acid  does  react  readily.  The 
equations  are : 

zinc  +  hydrochloric  acid  — *-  zinc  chloride  +  hydrogen 
iron  +  hydrochloric  acid  — >-  iron  chloride  •+-  hydrogen 

In  these  actions  the  metal  replaces  the  hydrogen  in  the 
acid,  forming  a  chloride. 

86.  Typical  Properties  of  Acids.  —  The  compounds  com- 
monly known  as  acids  are  characterized  by  certain 


CHLORIDES  83 

erties.  Acids  are  substances  that  contain  hydrogen  which 
may  be  replaced  by  metals  and  whose  water  solutions  turn 
litmus  red.  Substances,  such  as  sugar,  whose  hydrogen 
cannot  be  replaced  by  metals,  are  not  classed  as  acids. 
In  general, 

metal  +  acid  — »-  salt  of  the  metal  +  hydrogen 

When  an  acid  reacts  with  a  metal,  hydrogen  is  liberated 
and  is  generally  evolved  as  a  gas  unless  there  is  an  oxidiz- 
ing agent  in  the  solution,  in  which  case  the  hydrogen  may 
be  oxidized  to  water.  The  compound  formed  by  the  re- 
placement of  the  hydrogen  of  an  acid  by  a  metal  is  called 
a  salt.  The  salt  is  usually  found  dissolved  in  the  water 
that  was  used  to  dilute  the  acid.  The  portion  of  an 
acid  molecule  remaining  after  the  hydrogen  has  been 
removed  is  called  an  acid  radical.  A  salt,  then,  is  a  metal 
combined  with  an  acid  radical. 

The  sour  taste  of  acids  is  an  interesting  but  not  an  im- 
portant distinguishing  property.  Many  fruits  owe  their 
sour  taste  to  the  presence  of  acids.  Vinegar  is  hardly  more 
than  a  dilute  solution  of  acetic  acid.  The  change  in 
color  of  litmus  and  of  other  organic  coloring  matters  is  a 
convenient  way  of  recognizing  acids,  but  is  not  reliable  in 
all  cases. 

87.  Chlorides.  —  Hydrochloric  acid,  like  chlorine,  reacts 
with  many  metals,  forming  chlorides. 

metal  +  hydrochloric  acid — >-metallic  chloride  +  hydro'gen 
metal  4-  chlorine  — >- metallic  chloride 

All  the  common  chlorides  are  readily  soluble  in  water 
except  three  :  silver  chloride,  mercurous  chloride,  and  lead 
chloride.  The  metals  having  insoluble  chlorides  do  not  react 
with  the  add. 


84  HYDROCHLORIC  ACID 

*--^''^    J&V  • 

88.  Test  for  a  Chloride.  —  The  insolubility  of  silver  chlo- 
ride is  used  as  a  means  of  identifying  soluble  chlorides. 
If  a  solution  of  silver  nitrate  is  added  to  a  solution  of  a 
chloride,  a  white,  curdy  solid  separates ;  this  precipitate 
darkens  in  the  light.     By  a  precipitate  we  mean  a  solid 
resulting  from  a  chemical  action  in  solution,  that  separates 
because  it  is  insoluble. 

chloride  of  a  metal  +  silver  nitrate  — >- 

nitrate  of  the  metal  +  silver  chloride 

**     -  *  A    .{'i.  I       ••:••     :    fy 

Addition  of  silver  nitrate  causes  a  white  precipitate  in 
many  other  solutions,  but  silver  chloride  is  insoluble  in 
dilute  nitric  acid.  As  hydrochloric  acid  is  a  solution  of 
hydrogen  chloride,  the  same  test  together  with  the  litmus 
test  serves  to  identify  it. 

89.  Uses  of  Hydrochloric  Acid.  —  Very  small  quantities 
of  hydrochloric  acid  are  found  in  the  gastric  juice  and  are 
necessary  in  the  gastric  digestion.     It  is  often  given  as  a 
medicine  in  certain  cases  of  indigestion.     Large  quantities 
of  hydrochloric  acid  are  employed  in  the  preparation  of 
chlorine  to  be  used  in  the  manufacture  of  bleaching  powder. 
It  is  also  used  in  the  making  of   chlorides,  in   cleaning 
metals,  and  in  the  manufacture  of  glue  and  gelatine. 

90.  Proportion  of  Hydrogen  in  Hydrogen  Chloride.  —  When 
sodium  is  placed  in  hydrogen  chloride,  a  violent  reaction 
occurs,  during  which  the  sodium  replaces  the  hydrogen. 
The  reaction  can  be  made  less  energetic  by  using  sodium 
amalgam  instead  of  sodium.     Sodium  chloride,  mercury, 
and  hydrogen  result  from  the  reaction.     The  volume  of 
the  hydrogen  remaining  after  the  reaction  is  found  to  be 
one  half  that  of  the  hydrogen  chloride  taken. 

The  experiment  can  be  performed  in  the  following  man- 


COMPOSITION  OF  HYDROGEN  CHLORIDE 


85 


ner  :  hydrogen  chloride  is  generated  by  causing  sulphuric 
acid  to  drop  slowly  into  concentrated  hydrochloric  acid 
(Fig.  33,  A).  As  a  result  of  the  action  of  the  sulphuric 
acid  with  the  water,  gaseous  hydrogen  chloride  is  evolved. 
It  is  then  dried  by  being  made  to  pass  through  concen- 
trated sulphuric  acid.  A  glass  tube,  about  70  cm.  long 
and  1.5  cm.  in  diameter,  is  filled  with  the  dry  hydrogen 
chloride  by  the  displacement  of  mercury. 


0 


A  B  G 

FIG.  33.  —  VOLUME  COMPOSITION  OF  HYDROGEN  CHLORIDE. 

a,  cork  to  prevent  heating  tube  while  handling  ;    b,  sodium   amalgam ; 
c,  rubber  band  ;  d,  rubber  stopper. 

Sodium  amalgam  is  dropped  into  the  tube  of  hydrogen 
chloride  and  the  mouth  of  the  tube  instantly  closed  with 
a  stopper  (Fig.  33,  B).  The  tube  is  then  inverted  sev- 
eral times  in  succession,  its  mouth  placed  under  some 
water  in  a  tall  cylinder,  and  the  stopper  removed  (Fig. 
33,  0).  Water  rushes  into  the  tube. 

The  remaining  gas  (hydrogen)  is  brought  under  atmos- 
pheric pressure  by  raising  or  lowering  the  tube  in  the  cyl- 
inder until  the  liquid  on  the  inside  of  the  tube  is  at  the 
same  level  as  that  outside.  A  small  rubber  band  is  then 
placed  on  the  tube  at  the  surface  of  the  liquid. 


86 


HYDROCHLORIC  ACID 


The  volume  occupied  by  the  hydrogen  is  then  found 
by  measurement  to  be  one  half  that  occupied  by  the 
hydrogen  chloride.  This  gives  no  data  in  regard  to  the 
volume  occupied  by  the  chlorine. 

91.   Relative    Composition   of   Hydrogen   Chloride.  -  -  The 

composition   by   volume    can   be    shown   by   the   use   of 

the  electrolysis  apparatus 
shown  in  Fig.  34.  Hy- 
drochloric acid,  having  a 
specific  gravity  of  1.1,  is 
placed  in  the  tubes  a.  The 
three-way  stopcocks  b  are 
turned  so  that  there  is  a 
passage  from  c  to  d  and  a 
saturated  solution  of  so- 
dium chloric  is  drawn 
from  the  dishes  i  into  the 
collecting  tubes  e  until  they 
are  filled.  The  stopcocks 
are  then  turned  so  that 
there  is  a  passage  from  f  to 
d.  The  current  is  turned 
on,  and  as  soon  as  the  hy- 
drochloric acid  above  the 
anode  is  saturated  with 


FIG.   34.  —  ELECTROLYSIS   OF    HYDRO- 
CHLORIC ACID. 

chlorine,  the  stopcocks  are 

turned  so  that  the  hydrogen  and  chlorine  will  pass  into 
the  collecting  tubes  e.  When  the  upper  surfaces  of  the 
sodium  chloride  solution  are  just  above  the  support  #,  it  is 
inclined,  if  need  be,  so  as  to  mark  the  relative  height  of 
the  solution  in  the  collecting  tubes.  The  lower  support  h 
is  then  made  parallel  with  g.  The  solutions  in  ee  between 
g  and  h  are  displaced  in  the  same  time,  showing  that  equal 


SUMMARY  87 

volumes  of  hydrogen  and  chlorine  are  obtained  by  the 
electrolysis  of  hydrochloric  acid. 

92.   Volumetric  Composition  of  Hydrogen  Chloride.  —  In  the 

electrolysis  of  hydrogen  chloride  solution  just  described, 
we  have  shown  that  the  volume  of  the  hydrogen  set  free 
is  equal  to  the  volume  of  the  chlorine.  By  the  sodium- 
amalgam  method,  the  volume  of  the  hydrogen  chloride  was 
found  to  be  twice  the  volume  of  the  hydrogen.  Hence  we 
may  represent  the  volumetric  composition  of  hydrogen 
chloride  by  the  equation : 

1  volume  of  hydrogen  4- 1  volume  of  chlorine 

— >-2  volumes  of  hydrogen  chloride 

SUMMARY 

Hydrogen  chloride  may  be  prepared:  (1)  by  direct  union  of  its 
elements ;  (2)  by  the  action  of  sulphuric  acid  with  a  chloride.  The 
latter  is  the  common  method. 

It  is  a  gas  with  a  pungent  odor.  One  liter  under  standard  con- 
ditions weighs  1.64  grams.  One  liter  of  water  at  20°  dissolves  450 
liters  of  hydrogen  chloride. 

The  dry  gas  is  inactive;  its  water  solution  is  a  typical  acid. 

The  replacement  of  the  hydrogen  by  a  metal  gives  a  chloride.  All 
but  three  of  the  common  chlorides  are  soluble  in  water. 

Acids  contain  hydrogen  that  can  be  replaced  by  a  metal.  Their 
vater  solutions  turn  litmus  red  and  usually  have  a  sour  taste. 

Two  liters  of  hydrogen  chloride,  when  decomposed,  yield  one 
liter  of  hydrogen  and  one  liter  of  chlorine. 

The  chief  uses  of  hydrochloric  acid  are  for  the  preparation  of 
chlorine  and  chlorides,  and  for  cleansing  metals. 


88  HYDROCHLORIC  ACID 

EXERCISES 

1.  Why  is  not  the  direct  union  of  hydrogen  and  chlorine  a 
convenient  method  of  making  hydrogen  chloride  ?  ^ 

2.  Should  hydrogen   chloride    be    collected  by  upward   or 
downward  displacement  ? 

3.  Give  a  reason  for  the  use  of  each  substance  employed  in 
the  preparation  of  hydrogen  chloride. 

4.  State  and  explain  the  general  method  for  preparing  vol- 
atile acids. 

5.  Why  is  tin  moistened  with  a  solution  containing  hydro- 
chloric acid  before  being  soldered  ? 

6.  When    chlorine    is    brought    in    contact  with   ammonia, 
which  is  a  compound  of  hydrogen  and  nitrogen,  a  reaction 
occurs.     Name  one  compound  formed. 

7.  What  products  are  formed  when  metallic  magnesium  is 
treated  with  hydrochloric  acid  ? 

8.  What  is  formed  when  an  amalgam   of  potassium  ^ and 
mercury  is  exposed  to  hydrogen  chloride  ? 

9.  How   would   you   determine   whether   or  not   a   gas    is 
hydrogen  chloride  ? 

10.  State  the   difference   between  hydrogen   chloride   and 
hydrochloric  acid. 

11.  Name  two  metals  that  replace  hydrogen  in  dilute  hydro- 
chloric acid  and  two  that  do  not. 

12.  Give   three   distinct  characteristics  of  acids   in  water 
solution. 

13.  State  the  properties  that  cause  hydrochloric  acid  to  be 
called  a  typical  acid. 

14.  What  is  a  salt  ?     A  chloride  ?     An  acid  ? 

15.  How  could  you  determine  whether  an  unknown  sub- 
stance were  a  chloride  ?     Whether  it  were  hydrochloric  acid  ? 

16.  Give  the  volume  composition  of  hydrogen  chloride  and 
state  how  it  is  determined. 

*i\y 


CHAPTER  X 

MOLECULAR  COMPOSITION 

93.  Volume  Relation  of  Gases.  —  It  has  been  shown  in  the 
volumetric  synthesis  of  steam  (§  42)  that 

1    volume    of    oxygen    with    2    volumes   of  hydrogen 

gives  2  volumes  of  steam. 
1    volume    of    chlorine    with    1    volume   of   hydrogen 

gives  2  volumes  of  hydrogen  chloride  (§  92). 

The  study  of  the  actions  of  other  gases  gives  similar 
results  ;  thus  : 

1   volume   of  nitrogen   with   3   volumes   of   hydrogen 
gives  2  volumes  of  ammonia. 

In  these  cases  the  ratio  of  the  volumes  of  the  gases  that 
combine  may  be  expressed  in  whole  numbers  ;  this  is  also 
true  of  the  ratio  of  the  volume  of  each  of  the  combining 
gases  to  the  volume  of  the  product. 

94.  Law  of  Gay-Lussac.  —  The  relations   stated  in  §  93 
were  first  generalized  by  Gay-Lussac  in  his  law  of  volumes  : 
The  relative  combining  volumes  of  gases  and  the  volume  of 
the  product,  if  gaseous,  may   be  expressed  by  small   whole 
numbers.      Two  other  generalizations  relative  to  gases  are: 

Boyle's  Law  :  the  volume  of  any  gas  varies  inversely  as 
the  pressure,  if  the  temperature  remains  the  same  ;  and 
'    Charles'  Law  :  the  volume  of  any  gas  varies  directly  as 
the  absolute  temperature,  if  the  pressure  remains  the 
same.  , 

89 


90  MOLECULAR   COMPOSITION 

95.  Reacting  Weights  and  Volume  Weights  of  Gases.  —  We 

found  that  a  volume  of  chlorine  weighs  35.5  times  as  much 
as  an  equal  volume  of  hydrogen,  if  the  comparison  is  made 
under  similar  conditions  of  temperature  and  pressure. 
Similarly  we  found  that  oxygen  weighs  16  times  as  much 
as  hydrogen.  The  weights  of  equal  volumes  of  oxygen 
and  chlorine  are,  then,  as  16  to  35.5.  It  will  be  noticed 
that  these  numbers  are  reacting  weights  of  the  elements. 
A  similar  regularity  is  found  in  the  case  of  other  gaseous 
elements.  Hence  we  make  the  general  statement  that 
the  ratio  of  the  weights  of  equal  volumes  of  gaseous  elements 
is  the  same  as  the  ratio  of  certain  of  their  reacting  weights. 

96.  Avogadro's  Hypothesis.  — These  four  uniformities  in 
the  behavior  of  gases  led  Avogadro  in  1811  to  make  the 
following  hypothesis  :    Equal  volumes  of  gases  under  like 
conditions  of  temperature    and  pressure    contain   the  same 
number  of  molecules.     That  is  to  say,  a  liter  of  hydrogen 
contains  just  as  many  molecules  as  a  liter  of  oxygen,  a 
liter  of  chlorine,  a  liter  of  hydrogen  chloride,  or  a  liter 
of  any  other  gas  measured  under  the  same  conditions  of 
temperature  and  pressure. 

The  actual  number  of  molecules  in  the  liter  of  any  gas 
is  very  great,  but  we  have  no  concern  with  the  actual 
number.  We  know  nothing  whatever  of  the  number  of 
molecules  in  equal  volumes  of  solids  or  of  liquids. 

97.  Number  of  Atoms  in  the  Molecules  of  Gaseous  Ele- 
ments. —  In  a  former  chapter  (cf .  §  71)  we  showed  that  if 
we  knew  the  number  of  atoms  of  each  element  in  a  mole- 
cule, we  could  determine  the  relative  weight  of  the  atoms. 
We  cannot  count  the  number  of  atoms  in  a  molecule,  but 
by  means  of  Avogadro's  hypothesis  we  can  arrive  at  a 
definite  belief  in  the  matter. 


ATOMS  IN  GASEOUS  MOLECULES  91 

Experiment  shows  that  one  volume  of  chlorine  and  one 
volume  of  hydrogen  combine  to  form  two  volumes  of 
hydrogen  chloride. 

1  volume  of  hydrogen  +  1  volume  of  chlorine 

— >-  2  volumes  of  hydrogen  chloride 

Suppose  the  given  volume  of  hydrogen  contains  100Q 
molecules,  then  by  Avogadro's  hypothesis,  1006v  molecules 
must  also  be  contained  in  an  equal  volume  of  chlorine  ; 
and'  likewise,  since  the  hydrogen  chloride  occupies  twice 
the  space  of  the  hydrogen,  the  volume  of  hydrogen 
chloride  resulting  from  the  combination  must  contain  20()Q 
molecules.  Or,  briefly  stated: 

lOCK^  molecules  of  hydrogen  +  10BQ  molecules  of 

chlorine  — >-  20tX)  molecules  of  hj'drogen  chloride 

In  each  of  these  20$0  molecules  of  hydrogen  chloride 
there  must  be  some  hydrogen,  at  least  0w£_atom.  (cf.  §  68). 
At  least  2000,  atoms  of  hydrogen  have,  therefore,  been 
obtained  from  the  lO1^  molecules  of  hydrogen.  In  other 
words,  the  experiment  indicates  that  each  hydrogen 
molecule  splits  into  at  least  two  parts  during'  the  chemical 
action.  These  parts  cannot  be  smaller  than  atoms,  since 
atoms  are  indivisible.  Consequently,  each  hydrogen 
molecule  contains  at  least  two  atoms  of  hydrogen.  Similar 
reasoning  shows  that  the  chlorine  molecule  also  contains  at 
least  two  atoms. 

It  is  to  be  noted  that  any  even  number  might  be  used 
instead  of  two,  but  since  there  is  no  chemical  action  known 
in  which  either  the  hydrogen  or  the  chlorine  molecule 
seems  to  divide  into  more  than  two  parts,  it  is  not  proba- 
ble that  there  are  more  than  two  atoms  in  either  of  these 
molecules. 

Let  us  consider  the  composition  of  steam.     Experiment 


92  MOLECULAR    COMPOSITION 

shows  that  two  volumes  of  hydrogen  with  one  volume  of 
oxygen  yield  two  volumes  of  steam.  Assuming  1Q$0 
molecules  to  a  volume,  and  reasoning  according  to  Avoga- 
dro's  hypothesis,  the  two  volumes  of  hydrogen  and  of  steam 
must  each  contain  20$^ molecules.  Then: 

20(^0  molecules  of  hydrogen  +  10,00  molecules  of  oxygen 
— >-  2000  molecules  of  steam 

In  each  of  these  2000  molecules  of  steam,  there  must  be 
at  least  one  atom  of  oxygen. 

Not  less  than  2000  atoms  of  oxygen  have,  therefore, 
been  obtained  from  the  1000  molecules  of  oxygen.  Con- 
sequently, each  oxygen  molecule  contains  at  least  two  atoms 
of  oxygen.  It  has  been  already  shown  that  the  hydrogen 
molecule  contains  at  least  two  atoms.  The  steam  molecule, 
then,  must  contain  at  least  one  oxygen  atom  and  two 
hydrogen  atoms. 

While  the  molecules  of  all  the  common  gaseous  elements 
contain  two  atoms,  this  is  not  true  of  all  elements  in  the 
gaseous  state.  For  example,  mercury  and  zinc  have  each 
one  atom  to  the  molecule ;  phosphorus  has  four ;  and 
sulphur  eight,  six,  or  two,  according  to  the  temperature. 

SUMMARY 
Uniformities  in  the  Behavior  of  All  Gases : 

Boyle's  Law :  The  volume  of  any  gas  varies  inversely  as  the 
pressure  if  the  temperature  remains  the  same. 

Charles'  Law :  The  volume  of  any  gas  varies  directly  as  the 
absolute  temperature  if  the  pressure  remains  the  same. 

Gay-Lussac's  Law:  The  relative  combining  volumes  of  gases 
and  the  volume  of  the  product,  if  gaseous,  may  be  expressed  by 
small  whole  numbers. 


EXERCISES  93 

The  weights  of  equal  volumes  of  gaseous  elements  are  to  each 
other  as  certain  of  their  reacting  weights. 

The  uniformities  in  the  behavior  of  all  gases,  independent  of 
their  chemical  composition,  leads  to  the  belief  that  equal  volumes 
of  gases,  under  the  same  conditions  of  temperature  and  pressure, 
contain  the  same  number  of  molecules.  (Avogadro's  Hypothesis.) 

It  follows  from  Avogadro's  hypothesis,  and  from  the  volumetric 
composition  of  gaseous  compounds,  that  the  elements  hydrogen; 
oxygen,  chlorine,  and  nitrogen  each  have  two  atoms  to  the  mole- 
cule. Zinc  and  mercury  have  one  atom  to  the  mblecule ;  phos- 
phorus and  arsenic  have  four. 


EXERCISES 

1.  What  uniformities  (laws)  are  known  about  the  physical 
and  chemical  behavior  of  gases  ? 

2.  What  are  the  evidences  in  support  of  Avogadro's  hypoth- 
esis ? 

3.  Show  how  Gay-Lussac's  Law  of  Volumes  applies  to  the 
union  of  hydrogen  and  chlorine. 

4.  Show  by  Gay-Lussac's  Law  that  there  always  must  be 
some  oxygen  left  when  you  attempt  to  combine  three  volumes 
of  hydrogen  with  an  equal  volume  of  oxygen. 

5.  One  liter  of  marsh  gas  in  burning  combines  with  two 
liters  of  oxygen.     How  many  molecules  of  oxygen  are  needed 
to  react  with  one  molecule  of  marsh  gas  ? 

6.  Approximately  what  are  the  relative  numbers  of  mole- 
cules of  oxygen  and  nitrogen  in  air  ? 

7.  What  volume  of  air  is  needed  for  the  complete  combus- 
tion of  100  c.c.  of  marsh  gas  ? 

/ 

8.  Two  molecules  of  nitric  oxide  (gas)  unite  with  one  mole- 
cule of  oxygen  when  the  two  are  brought  together.    How  many 
cubic  centimeters  of  oxygen  would  be  needed  for  complete  re- 


94  MOLECULAR   COMPOSITION 

action  with  64  c.c.  of  nitric  oxide  ?     How  much  air  would  bo 
needed  for  the  same  purpose  ? 

9.    Give   reasons  for  believing  that  the  oxygen  molecule 
contains  at  least  two  atoms. 

10.  One   volume  of  hydrogen  unites  with  one  volume  of 
bromine  gas,  forming  two  volumes  of  hydrogen  bromide.    How 
many  atoms  are  there  in  the  molecule  of  gaseous  bromine?  ; 
Explain. 

11.  Two  tanks  of  equal  capacity  contain  oxygen.     The  gas 
in  the  first  is  under  atmospheric  pressure ;  that  in  the  second 
is  under  3.2  atmospheres'  pressure.     How  does  the  weight  of 
oxygen  in  the  second  tank  compare  with  the  weight  of  that  in 
the  first  ? 

12.  When  two  volumes  of  hydrogen  chloride  are  decomposed 
by  sodium  amalgam,  they  yield  one  volume  of  hydrogen.     As- 
suming 3000  molecules  to  one  volume,  show  how  Avogadro's 
hypothesis  can  be  used  to  prove  the  composition  of  the  hydro- 
gen molecule. 

13.  Why  is  the  principle  of  Avogadro  a  hypothesis  rather 
than  a  law  ? 


CHAPTER  XI 
ATOMIC  AND  MOLECULAR  WEIGHTS 

98.  Atomic  Weights.  —  Since  it   has   been   shown    that 
there  are  twice  as  many  hydrogen  atoms  as  oxygen  atoms 
in  the  molecule  of  steam,  the  weight  of  the  oxygen  atom 
relative  to  the  weight  of  the  hydrogen  atom  can  now  be 
determined.     The  oxygen  in  water  weighs  eight  times  as 
much  as  the  hydrogen.     The  weight  of  the  hydrogen  atom 
is  taken  as  the  unit  in  comparing  the  weights  of  the  atoms 
of  different  elements1 ;  therefore,  the  two  hydrogen  atoms 
contained  in  a  molecule  of  water  must  have  a  weight  of  2. 
The  one  oxygen  atom  combined  with  the  two  hydrogen     -. 
atoms  must  weigh  8  x  2,  or  16.     The  atomic  weight  of 
hydrogen  is  1  ;  of  oxygen,  16.      The  atomic  weight  of  an 
element  is  a  number  which  expresses  how  many  times  its 
atom  is  as  heavy  as  the  hydrogen  atom.     It  corresponds  to 

one  of  the  reacting  weights. 

99.  Density  and  Specific  Gravity.  —  By  the   density  of  a 
substance  is  meant  the  number  of  units  of  mas's  that  oc- 
cupy a  unit  volume.     In  scientific  work  the  gram  is  the 
unit  of  massV  and  the  cubic  centimeter  the  unit  of  volume. 
The  density  of  a  substance,  then,  is  the  number  of  grams 
of  that  substance  occupying  one  cubic  centimeter.     One 
gram  of  water  at  4°  C.  occupies  one  cubic  centimeter. 

1  In  tables  of  exact  atomic  weight  in  common  use,  the  standard  actually 
taken  is  oxygen  =  16.00.  This  makes  the  atomic  weight  of  hydrogen 
slightly  greater  than  1 .  For  ordinary  purposes,  however,  the  hydrogen 
standard  of  1  is  satisfactory. 

95 


96  ATOMIC  AND  MOLECULAR    WEIGHTS 

The  specific  gravity  of  a  substance  is  the  weight  of  that 
substance  divided  by  the  weight  of  an  equal  volume  of 
some  substance  taken  as  a  standard.  Water  is  taken  as 
the  standard  of  specific  gravity  for  liquids  and  solids.  The 
term  density  is  often  used  incorrectly  for  specific  gravity. 

100.  Specific  Gravity  and  Vapor  Density  of  Gases.  —  There 
are  two  standards  for  the  specific  gravity  of  gases,  air  and 
hydrogen.     For  experimental  purposes  air  is  commonly 
used ;   for  purposes  of  calculation  hydrogen  is  more  con- 
venient.    The  term  specific  gravity  of  a  gas,  when  used 
without  explanation,  means  the  number  of  times  the  gas 
is  as  heavy  as  an  equal  volume  of  air.     The  term  vapor 
density  means  the  specific  gravity  of  a  gas  with  respect  to 
hydrogen.      Vapor  density  is  the  number  of  times  a  gas  is 
as   heavy   as   an   equal  volume   of  hydrogen.     The  vapor 
density  of  a  gas  is  found  by  determining  the  weight  of  a 
liter  of  the  gas  and  comparing  this  weight  with  the  weight 
of  a  liter  of  hydrogen  under  the  same  conditions  of  tem- 
perature and  pressure.     Such  comparisons  of  the  weights 
of  equal  volumes  of  gases  can  be  made  at  any  convenient 
temperature  and  pressure.     The  usual  custom,  however, 
is  to  compare  weights  of  equal  volumes  at  0°  C.  and  760 
mm. ;  that  is,  at  standard  conditions.     In  the  determina- 
tion of  specific  gravity,  great  care  must  be  taken  to  have 
the  gases  pure  and  dry. 

101.  Determination  of  Molecular  Weights.  —  The  molecular 
weight  of  a  substance  is  a  number  which  expresses  how  many 
times  its  molecule  is  as  heavy  as  the  hydrogen  atom. 

It  follows  from  Avogadro's  hypothesis  that  the  weights 
of  equal  volumes  of  two  gases  will  have  the  same  ratio  as 
the  weights  of  their  molecules.  This  can  be  shown  by  the 
following  reasoning.  One  liter  of  hydrogen,  measured 


Theodore  W.  Richards  was 

born  in  Germantown,  Penn- 
sylvania. He  is  now  Erving 
Professor  of  Chemistry  in 
Harvard  University.  His  re- 
visions of  the  atomic  weights  of 
more  than  a  score  of  elements 
have  been  accorded  world- 
wide recognition.  His  later 
researches  have  dealt  with 
atomic  volumes,  electrochem- 
ical and  thermochemical  be- 
havior of  the  elements,  and 
compressibility  of  th,e  atoms.,  • 


Edward    W.    Morley  was 

born  in  1838  at  Newark,  New 
Jersey.  He  graduated  at 
Williams  and  in  1869  became 
Professor  of  Chemistry  in 
Western  Reserve  University. 

He  has  explored  fields  in 
both  physics  and  chemistry. 
His  greatest  achievement  was 
the  determination  of  the  exact 
ratio  by  which  oxygen  and 
hydrogen  combine  by  weight, 
as  this  ratio  has  been  generally 
accepted. 


A,  ft 

w. 


DETERMINATION  OF  MOLECULAR    WEIGHTS      97 


under  standard  conditions,  weighs  0.09  gram;  one  liter 
of  oxygen,  measured  under  similar  conditions,  weighs 

1.43  grams.     The  liter   of  oxygen  is   r1^  or  almost  16 

0.09 

times  as  heavy  as  a  liter  of  hydrogen.  If  there  are  n 
molecules  in  a  liter  of  oxygen,  there  must  be,  according 
to  Avogadro's  hypothesis,  n  molecules  in  a  liter  of  hydro- 
gen. Since  n  molecules  of  oxygen  weigh  16  times  as 
much  as  n  molecules  of  hydrogen,  one  molecule  of  oxy- 
gen  must  weigh  16  times  as  much  as  one  molecule  of  hy- 
drogen. 

The  hydrogen  molecule  we  showed  to  contain  two  atoms, 
hence  its  molecular  weight  is  2.  The  molecular  weight  of 
oxygen  is,  therefore,  16  x  2,  or  32.  Thus  we  see  that  the 
molecular  weight  of  a  gas  must  be  twice  its  vapor  density. 
As  chlorine  is  35.5  as  dense  as  hydrogen,  its  molecule 
weighs  71  times  as  much  as  an  atom  of  hydrogen.  We 
have  proved  that  the 
chlorine  molecule  con- 
tains two  atoms,  so  the 
atom  of  chlorine  weighs 
35.5  times  as  much  as 
an  atom  of  hydrogen. 

102.  Alternative 
Method  for  Determina- 
tion of  Molecular 
Weights.1  -  -  A  gram- 
molecular  weight  of  a 
gas  is  as  many  grams 
of  that  gas  as  there  are 
units  in  its  molecular  weight.  The  molecular  weight  of 
hydrogen  is  2.  Two  grams  is  a  gram  -molecular  weight  of 

1  The  instructor  is  advised  to  have  the  class  omit  either  paragraph  101 
or  paragraph  102.     The  use  of  both  methods  may  confuse  beginners. 


FIG.  35.  —  GRAM-MOLECULAR  VOLUME. 


.try*'.  :  z  y**  :  /MM^  \  / 

98  ATOMIC  AND  MOLECULAR    WEIGHTS 

hydrogen.  Since  one  liter  of  hydrogen  weighs,  under 
standard  conditions,  0.09  gram,  two  grams  of  hydrogen 
will  occupy  2-4-0.09,  or  221S  liters  (Fig.  35). 

The  gram-molecular  weight  of  any  gas  occupies  this  same 
volume.  This  is  shown  by  the  following  considerations. 
A  gram-molecular  weight  of  a  gas  equals  2  grams  mul- 
tiplied by  the  vapor  density  (V.  D.)  of  the  gas  (§  100). 
Since  the  vapor  density  of  a  gas  is  the  number  of  times 
that  gas  is  as  heavy  as  an  equal  volume  of  hydrogen,  the 
weight  of  1  liter  of  any  gas  is  equal  to  the  weight  of  1 
liter  of  hydrogen  (.09  g.)  multiplied  by  the  vapor  density 
of  the  gas.  Now,  2  grams  of  hydrogen  occupies  22.^  liters 

at  standard  conditions  f— —  =  22.^J,  and,  according  to  the 

statements  just  made,  the  relations  shown  by  the  following 
equalities  will  also  hold  : 

gram-molecular  weight  of  any  gas       2  g.  x  V.  D.         2  g. 
weight  of  1  liter  of  that  gas        =  .09  g.  x  V.  D.  =  .09  g. 

=  22.5  liters 

Therefore,  a  gram-molecular  weight  of  any  gas  occupies  a 
volume  of  22.^  liters.  ^ 

2  grams  of  hydrogen  have  a  volume  of  2j2.$  liters. 
32  grams  of  oxygen  have  a  volume  of  22. §  liters. 
71  grams  of  chlorine  have  a  volume  of  22.5  liters.          ^ 
36.5  grams  of  hydrogen  chloride  have  a  volume  of  22.^ 

liters. 

Therefore,  32,  71,  and  36.5  are  respectively  the  molecular 
weights  of  oxygen,  chlorine,  and  hydrogen  chloride. 

If  82  c.c.  (0.082  liter)  of  carbon  dioxide  weigh  0.1623 
gram,  we  can  find  the  weight  of  22.^  liters  by  the  propor- 
tion : 

* 
0.082  liter  :  22.^  liters  ::  0.1623  gram  :  x  gram 

#  =  44  grams 


ATOMS  IN  THE  MOLECULE   OF  A    COMPOUND     99 

Therefore,  the  weight  of  the  carbon  dioxide  molecule  is  44. 
It  is  44  times  as  heavy  as  the  hydrogen  atom. 

103.  Determination  of  the  Number  of  Atoms  in  the  Molecule 
of  a  Compound.  —  We  have  shown  how  the  number  of  atoms 
in  a  molecule  of  a  gaseous  element  is  determined  in  the 
cases  of  hydrogen,  oxygen,  and  chlorine  (cf.  §  97).  When 
the  gas  is  a  compound,  we  can  find  how  many  of  each 
kind  of  atoms  are  present  by  ascertaining 

(a)  the  composition  by  weight ; 

(5)  the  molecular  weight. 

In  the  case  of  carbon  dioxide  : 

(a)  its  composition  by  weight  is  27.3  %  carbon,  72.7  % 
oxygen  ; 

(6)  its  molecular  weight  is  44,  as  shown  above. 

The  weight  of  the  oxygen  in  the  molecule  is  72.7  %  of  44, 
or  32.  We  have  shown  that  the  atomic  weight  of  oxygen 
is  16,  so  there  must  be  two  atoms  of  oxygen  in  each  mole- 
cule of  carbon  dioxide. 

The  carbon  in  each  molecule  will  be  27.3%  of  44,  or  12. 
Carbon  cannot  be  vaporized,  consequently  we  cannot  de- 
termine its  atomic  weight  by  the  method  used  for  oxygen. 
However,  many  compounds  of  carbon  are  gases,  and  in  no 
case  does  the  carbon  furnish  less  than  twelve  parts  of  the 
molecular  weight.  That  is,  the  smallest  portion  of  carbon 
that  enters  into  chemical  combination  (the  atom)  weighs 
twelve  times  as  much  as  the  hydrogen  atom. 

The  carbon  dioxide  molecule  is  composed,  therefore,  as 
its  name  indicates,  of  one  atom  of  carbon  (weighing  12) 
and  two  atoms  of  oxygen. 


100  ATOMIC  AND  MOLECULAR    WEIGHTS 

SUMMARY 

It  follows  from  Avogadro's  hypothesis  that  the  vapor  densities 
of  gases  are  in  the  same  ratio  as  their  molecular  weights. 

The  molecular  weight  of  a  gas  can  be  calculated  by  multiplying 
the  molecular  weight  of  hydrogen,  2,  by  the  vapor  density  of  the 
gas.  The  vapor  density  of  a  gas  is  determined  experimentally. 

The  molecular  weight  of  a  gas  can  also  be  determined  by  mak- 
ing use  of  the  fact  that  the  gram-molecular  weights  of  all  gases 
have  the  same  volume,  22*  liters.  Knowing  the  weight  of  any 
given  volume  of  the  gas,  the  required  molecular  weight  can  be 
found  from  a  proportion  in  which  the  weight  and  volume  and  the 
number  22.jTare  the  three  known  quantities. 

The  molecular  weight  of  hydrogen  is  2,  of  oxygen  32,  of  chlo- 
rine 7 1 ,  of  nitrogen  28. 

PROBLEMS 

1.  A  liter  of  bromine  gas,  at   standard   conditions,  would 
weigh  7.2  grams.      What  is  its  vapor  density?     Using  the 
answer  to  question  10,  Chapter  X,  determine  the  atomic  weight 
of  bromine. 

2.  A  liter  of  marsh  gas,  at  standard  conditions,  weighs  0.72 
gram.     What  is  the  molecular  weight  of -marsh  gas  ? 

3.  Methane  gas  is  composed  of  carbon  75  %,  hydrogen  25  %, 
and  its  molecular  weight  is  16.     What  part  of  the  molecular 
weight  of  the  compound  is  carbon  ?     What  part  is  hydrogen  ? 
The  atomic  weight  of  carbon  is  12;  how  many  atoms  of  each 
element  are  there  in  a  molecule  of  the  compound  ?        C  /4 

4.  0.58  gram  of  acetylene  gas  has  a  volume  of  495.7  c.c., 
standard  conditions.     What   is    the  vapor   density  of  acety- 
lene ?     What  is  its  molecular  weight ?  (fa, t / J^ /,  /  y  -  $/,$•) 

5.  Determine  the  molecular  weight  of  the  following  sub- 
stances  : 


PROBLEMS 


101 


GAB 

WEIGHT  DATA 

290  c.c.  weighs  0.574  g.    u  .  3 

Hydriodic  acid.                .          .               •     • 

93  c.c.  weighs  0.531  g. 

Etli6r  f£ja,seous  conditions)     .     .     .    »     • 

230  c.c.  weighs  0.766  g.  -'*]  Lj- 

6.  Air  is  14.44  times  as  heavy  as  hydrogen.     Compute  the 
specific  gravity  of  the  gases  mentioned,  in  the  above  problems. 

7.  What  is  the  numerical  ratio   between  the   molecular 
weight  of  a  gas  and  its  vapor  density  ?    What  is  the  ratio  be-    . 

tween  the  molecular  weight  and  the  specific  gravity  ? 

rf  y  /u .  IJ  k  V 

8.  Determine  the  molecular  weights  of  the  following  gases : 


/v 


GAS 

Sr.  G.  (air) 

0.597 

Carbon  monoxide                                       •     «     • 

0.968 

1.806 

9.   50  c.c.  of  a  certain  gas  at  standard  conditions  weighs 
0.076  gram.     What  is  its  molecular  weight  ? 

10.  Compute  the  molecular  weight  of  nitrogen  from  the 
following  data :  222.5  c.c.  of  nitrogen  at  27°  C.  af.d  .730  mm. 
pressure,  weighs  0.25  gram. 

11.  If  540.1  c.c.  of  a  certain  gas,  when- "measured 'dry  aV, 
18°  C.  and  750  mm.  pressure,  weighs  1.71  grams,  what  is  the 
molecular  weight  of  the  gas  ? 


CHAPTER   XII 
CHEMICAL  FORMULAS  AND  NAMES 

104.  It  is  a  great  convenience  to  have  a  short,  accurate 
method  of  representing  the  chemical  changes  taking  place 
in  a  chemical  action.     We  have  been  expressing  those 
changes  in  the  form  of  equations,  in  which  we  have  on 
one  side  the  names  of  the  substances  which  enter  into  the 
action,  and  on  the  other  the  names  of  the  products  formed. 
According  to  the  atomic  theory,  chemical   action   takes 
place  between  molecules,  by  the  rearrangement  and  redis- 
tribution of  the  atoms.     If  we  express  the  action  in  terms 
of  molecules  and  atoms,  it  becomes  much  more  significant. 
Symbols  and  equations  are  used  to  represent  chemical 
actions  as  simply  as  possible. 

105.  Significance  of  the  Symbol.  — The  symbol  of  an  ele- 
ment is  usually  the  initial  letter  of  the  name  capitalized. 
Thus  one  atom  of  hydrogen  is  represented  by  a  capital  H, 
and  as  jthe:  a&orn  has  mass,  this  H  represents  also  a  definite 
'mass  oi'  iiydroge.ni  one  part  by  weight.     The  symbol  thus 
means  riot  only  -the  substance,  but  a  definite  quantity  of 
the  substance.     O  means  one  atom  of  oxygen,  also  sixteen 
parts  by  weight  of  oxygen. 

When  several  substances  have  the  same  initial,  another 
letter  conspicuous  in  the  name  is  added,  but  not  capital- 
ized, as  C  (carbon);  Ca  (calcium);  Cd  (cadmium);  Cl 
(chlorine).  In  some  cases  the  symbol  is  derived  from  a 
Latin  name,  as  Fe  (ferrum,  iron);  Cu  (cuprum,  copper); 
Na  (natrium,  sodium);  and  K  (kalium,  potassium). 

102 


SIGNIFICANCE   OF  THE  FORMULA  103 

106.  Significance  of  the  Formula.  —  The  formula  of  a 
molecule  is  formed  by  grouping  together  the  symbols  of  the 
atoms  composing  it.  The  molecule  of  hydrogen  chloride 
was  found  to  consist  of  one  atom  of  hydrogen  and  one 
atom  of  chlorine.  Its  formula,  therefore,  is  HC1.  This 
means 

(1)  one  molecule  of  hydrogen  chloride  ; 

(2)  that  the  molecule  of  hydrogen  chloride  contains  one 

atom  of  hydrogen  and  one  atom  of  chlorine ; 

(3)  that  one  molecule  of  hydrogen  chloride  is  composed  of 

1  part  by  weight  of  hydrogen  and  35.5  parts  by 
weight  of  chlorine ; 

(4)  36.5  parts  of  hydrogen  chloride  by  weight; 

(5)  1  part  by  volume  of  hydrogen  chloride  (Avogadro's 

hypothesis). 

When  a  molecule  contains  more  than  one  atom  of  the 
same  kind,  the  symbol  is  not  usually  repeated,  but  the 
number  of  the  atoms  is  written  as  a  subscript  to  the  sym- 
bol. The  formula  of  water  is  usually  written  H2O  and 
not  HOH.  As  stated  above,  H2O  means 

(1)  one  molecule  of  water  ; 

(2)  that  one  molecule  of  water  is  composed  of  two  atoms 

of  hydrogen  and  one  atom  of  oxygen ; 

(3)  that  one  molecule  of  water  is  composed  of  2  parts  by 

weight  of  hydrogen  and  16  parts  by  weight   of 
oxygen ; 

(4)  18  parts  by  weight  of  water ; 

(5)  1  part  by  volume  of  steam! 

It  is  only  when  the  compound  is  in  a  gaseous  state  that 
its  formula  represents  one  part  by  volume.  Thus,  NaCl 
represents  one  molecule  of  sodium  chloride  as  composed  of 


104  CHEMICAL  FORMULAS  AND  NAMES 

one  atom  of  sodium  and  one  atom  of  chlorine ;  that  is, 
23  parts  by  weight  sodium  and  35.5  parts  chlorine,  or  a 
total  weight  of  58.5  sodium  chloride.  It  also  represents 
one  volume  of  the  gaseous  salt,  but  not  of  the  solid  salt. 

107.  The  Number  of  Molecules  that  take  part  in  a  reac- 
tion is  represented  by  means  of  a  coefficient. 

2  HC1  =  2  molecules  hydrochloric  acid 

3  H2O  =  3  molecules  water 


CALCULATION   OF   THE  FORMULA 

108.  Method  when  Vapor  Density  is  Known.  —  If  we 

know  the  vapor  density,  the  composition  and  the  atomic 
weights,  we  can  calculate  the  molecular  weight  and  the 
formula. 

Example : 

The  vapor  of  alcohol  is  23  times  as  heavy  as  hydrogen. 
The  composition  of  alcohol  is:  carbon,  52.17%;  hydro- 
gen, 13.04%;  oxygen,  34.78%;  the  atomic  weights  are 
12,  1,  and  16  respectively.  Required  to  calculate  the 
formula. 

•'•A*~ 

Solution : 

j^/ Since  the  vapor  density  referred  to  hydrogen  is  23,  the 
molecular  weight  must  be  46  (cf.  §  101).  The  weight  of 
carbon  in  the  molecule  is  52.17  %  of  46,  or  24.  The  weight 
of  the  hydrogen  in  the  molecule  is  13.04%  of  46,  or  6. 
The.oxygen  is  34.'78%  of  46,  or  16, 

Since  one  atom  of  carbon  weighs  12,  there  must  be  two 
carbon  atoms  to  make  up  the  24  parts  of  carbon  in  the 
alcohol  molecule.  There  must  be  six  hydrogen  atoms,  as 
each  weighs  1,  and  as  an  oxygen  atom  weighs  16,  there  can 

OtsL&^-l       fyf 


Percentage                Weight  of  element 
composition                       in  molecule 

carbon       92.3             24 

Atomic 
weight 

12 

hydrogen    7.7 

2 

1 

CALCULATION  OF  THE  FORMULA  105 

be  but  one  of  these  atoms  in  the  molecule  of  alcohol. 
The  formula  for  the  alcohol  is  therefore  C2H6O. 

The  vapor  density  of  acetylene  is  13;  its  composition 
is  carbon,  92. 3  % ;  hydrogen,  7.7%.     What  is  its  formula ? 

Solution : 

Since  the  vapor  density  is  13,  the  molecular  weight  is  26. 

Number 
of  atoms 

2 
2 

»/  «— f 

Hence  the  formula  is  C2H2. 

This   method   can   be   used   only  when  the   molecular 
weight  can  be  determined  by  experimental  means. 

109.    Method  when  Molecular  Weight  is  not  Known.  — 

Since  the  oxygen  atom  weighs  16  times  as  much  as  the 
hydrogen  atom,  there  are  ^  as  many  atoms  in  1  gram  of 
oxygen  as  there  are  in  1  gram  of  hydrogen.  The  relative 
numbers  of  atoms  per  gram  of  several  elements  may  be 
calculated  by  dividing  1  gram  by  the  atomic  weight  of 
each  of  the  elements  in  question.  Likewise  it  is  true  that 
if  we  divide  any  given  weights  of  elements  by  their  respec- 
tive atomic  weights,  we  obtain  numbers  that  are  in  the 
ratio  of  the  numbers  of  atoms  present. 

The  percentage  composition  of  sulphuric  acid  is : 

hydrogen  2. 04  % 

.sulphur  32^65% 

oxygen  65.31% 

This  means  that  100   parts  by  weight  of  sulphuric  acid 

contain 

2.04  parts  by  weight  of  hydrogen, 
32.65  parts  by  weight  of  sulphur,  and 
65.31  parts  by  weight  of  oxygen. 


106  CHEMICAL  FORMULAS  AND  NAMES 

If  we  divide  the  parts  by  weight  of  each  of  these  elements 
respectively  by  its  atomic  weight,  we  obtain  the  relative 
number  of  atoms  in  the  molecule  of  the  compound. 

hydrogen  2.04 -f-  1  =  2.04 
sulphur  32.65  -5-  32  =  1.02 
oxygen  65.31  -r- 16  =  4.08 

For  every  2.04  atoms  of  hydrogen  it  contains,  sulphuric 
acid  must  contain  1.02  atoms  of  sulphur  and  4.08  atoms 
of  oxygen.  But,  since  not  less  than  1  atom  of  an  element 
can  enter  a  molecule  of  a  compound,  the  ratio  2.04 : 1.02 : 
4.08  must  be  reduced  to  the  smallest  possible  whole  num- 
bers, if  we  are  to  write  the  simplest  chemical  formula  that 
will  correspond  to  the  percentage  composition  of  sulphuric 
acid.  These  whole  numbers  may  be  found  by  dividing 
each  term  of  the  ratio  by  the  smallest  term. 

2.04  -f-  1.02  =  2  hydrogen 
1.02-5-1.02  =  1  sulphur 
4.08  -i- 1.02  =  4  oxygen 

H2SO4  is,  therefore,  the  simplest  formula  that  can  be  used 
to  represent  the  chemical  composition  of  sulphuric  acid 
In  many  cases  it  is  impossible  to  determine  the  molecular 
weight  by  vapor  density  or  other  experimental  methods. 
In  these  cases  the  simplest  (or  empirical)  formula  that 
agrees  with  the  percentage  composition  is  the  one  that  is 
accepted.  The  true  formula  for  sulphuric  acid  is  either 
H2SO4  or  some  multiple  of  H2SO4.  Since  this  formula 
corresponds  to  the  molecular  weight  of  sulphuric  acid,  that 
is  indicated  by  the  osmotic  pressure  (§  143)  of  its  solutions, 
and  since  its  general  behavior  indicates  that  it  contains  but 
2  hydrogen  atoms,  H2SO4  is  believed  to  be  the  correct 
formula. 


VALENCE  107 

The  formula  for  benzol  may  be  calculated  as  follows : 

Percentage  Atomic  Atomic  Simplest       Simplest  Corre- 

composition  weight      ratio     atomic          formula  spending 

ratio  molecular 

weight 

carbon       92.3%       12       7.7        1C  12 

hydrogen    7.7%         1        7.7        1       H  C  _1 

13 

But,  since  the  vapor  density  of  benzol  has  been  found 
by  experiment  to  be  39,  the  molecular  weight  of  benzol 
must  be  2  x  39,  or  78.  Now  78  is  six  times  13,  the 
molecular  weight  corresponding  to  the  formula  CH.  The 
true  formula  for  benzol  is,  therefore,  C6H6. 

'. 

110.  Calculation  of  the  Percentage  Composition  from  the 

Formula.  —  If  the  formula  of  a  compound  is  known,  and 
also  the  atomic  weights  of  the  elements  composing  it, 
the  percentage  composition  can  be  calculated.  Thus  the 
formula  of  an  iron  oxide  is  Fe2O3 ;  the  atomic  weight  of 
iron  is  56,  of  oxygen  16. 

The  formula  represents : 

2  x  56,  or  112  parts  by  weight  of  iron,  and 

3  x  16,  or    48  parts  by  weight  of  oxygen,  making 

160  parts  by  weight  of  iron  oxide. 

or  70  per  cent  by  weight  is  iron,  and 
or  30  per  cent  by  weight  is  oxygen. 

111.  Valence.  —  Among   the    hydrogen  compounds   we 
have  so  far  considered  is   hydrogen   chloride,  in  which 
the  chlorine  atom  holds  one  hydrogen  atom.      In  steam 
(H2O)  each  oxygen  atom  holds  two  hydrogen  atoms,  in 
ammonia  (NH3)  three  hydrogen  atoms  are  held  by  one 
other  atom,  and  in  methane  (CH4),  four.     Thus  atoms 


108  CHEMICAL  FORMULAS  AND  NAMES 

differ  in  their  ability  to  hold  other  atoms.  This  holding 
power  is  expressed  in  terms  of  the  power  of  the  atom  to 
hold  hydrogen  atoms.  The  valence  of  an  atom  is  the 
number  of  hydrogen  atoms  with  which  it  may  combine  or 
which  it  may  replace. 

Any  element  that  combines  with  hydrogen,  or  replaces 
it  atom  for  atom,  has  a  valence  of  one.  In  the  examples 
below,  it  will  be  seen  that  the  metal  replaces  the  hydrogen 
of  the  compound  directly,  atom  for  atom  : 

HC1,,     HBr,       HI, 
NaCV    AgBiy    KI.» 

If  an  element  combines  with,  or  replaces,  two  hydrogen 
atoms,  it  is  said  to  be  divalent,  that  is,  its  valence  is  two. 
A  knowledge  of  valence  is  an  aid  in  writing  formulas. 
Valence  will  be  considered  in  Chapter  XVI  in  connection 
with  a  different  property. 

Sodium,  potassium,  silver  have  a  valence  of  one.  Alu- 
minum usually  has  a  valence  of  three.  The  other  common 
metals  usually  have  a  valence  of  two. 

Chlorides  Oxides 

/  NaCl,-   KC1;  AgCl.  '        1  Na2O,-   K2O,-  Ag2O.  * 
:  ZnCl2;  CuCl2;  CaO,.    MgO.- 


AlClg.-  A12O3. 

112.  Variations  in  Valence.  —  An  element  may  have 
more  than  one  valence,  according  to  the  element  with 
which  it  combines,  and  the  conditions  under  which  the  com- 
bination takes  place.  The  valence  of  hydrogen  is  always 
regarded  as  one,  and  that  of  oxygen  as  two.  Sulphur 
has  a  valence  of  two  in  hydrogen  sulphide,  H2S  ;  in  sul- 
phur dioxide,  S02,  its  valence  is/ow,  being  twice  that  of 
oxygen  ;  in  sulphur  trioxide,  SO3,  its  valence  is  six. 


Johann  Jacob  Berzelius  (1779-1848)  was  a  Professor  of  Chem- 
istry in  Stockholm.  Although  hampered  by  lack  of  means,  he 
impressed  himself  and  his  ideas  on  the  scientific  world  and  became 
the  leading  figure  in  it. 

Berzelius  was  an  analytical  genius ;  he  repeated  the  work  and 
extended  the  laws  of  Dalton  to  organic  substances.  He  undertook 
the  determination  of  atomic  weights,  taking  the  weight  of  oxygen 
as  100.  His  accuracy  enabled  him  to  discover  several  elements. 
He  tried  to  explain  molecular  structure  and  developed  the  electro- 
chemical theory,  which,  though  later  modified  by  himself  and  others, 
has  proved  of  great  service.  He  introduced  the  use  of  initial  letters 
as  symbols  of  atoms. 


BINARY  COMPOUNDS  109 

CHEMICAL  NAMES 

The  names  of  substances  must  be  studied  in  connection 
with  the  substances  and  their  reactions.  The  principles 
involved  in  the  assignment  of  the  names  will  aid  in  their 
recognition  and  explanation. 

Chemical  names  are  based  largely  on  a  system  intro- 
duced by  a  friend  of  Lavoisier,  Guyton  de  Morveau, 
shortly  after  the  discovery  of  oxygen.  The  name  'of  a  sub- 
stance should  show  the  elements  of  which  it  is  composed  and, 
as  far  as  possible,  their  relative  proportions. 

113.  The  names  of  elements  are  not  based  on  any  princi- 
ple.    Some,  like  sulphur  and  silver,  are  very  old,  some 
are  named  for  countries  or  localities,  as  magnesium  and 
columbium.     Soda  and  alum  were  well-known  compounds 
and  when  metals  were  obtained  from  them  they  received 
the  names   of   sodium   and   aluminum.     Other  elements 
have  been  named  in  similar  manner.     Chlorine,  argon, 
radium,  and  chromium  are  named  from  peculiarities  pos- 
sessed by  them,  while  selenium  (moon),  tellurium  (earth), 
and  uranium  (heaven)  show  that  chemists  have  not  been 
without  poetic  fancy. 

Of  the  elements  discovered  more  recently,  the  metals 
have  received  names  ending  in  -ium,  the  non-metals  in  -n 
or  -ne.  The  names  have  usually  been  assigned  the  ele- 
ments by  their  discoverers  and  are  carried  practically 
unchanged  into  other  languages. 

114.  Binary  Compounds.  —  The  names  of  compounds  are 
formed  by  combining  the  names  of  the  constituents  into 
compound  words.     The  name  of  one  of  the  elements,  a 
metal  if  present,  is  used  adjectively  and  a  distinctive  part 
of  the  name  of  the  other  constituent  is  attached,  as  silver 
chloride,  iron  oxide,  sulphur  chloride. 


110  CHEMICAL  FORMULAS  AND  NAMES 

Binary  compounds  contain  only  two  elements  and  have 
names  ending  in  -ide. 

There  are  two  compounds  of  mercury  and  oxygen. 
The  one  containing  the  higher  oxygen  ratio  is  mercuric 
oxide,  the  one  with  the  less  oxygen  is  mercurpus  oxide. 
In  nitrous  oxide,  the  ratio  of  nitrogen  to  oxygen  is  7  :  4 ;  in 
nitric  oxide,  the  ratio  is  7:8.  In  general,  the  suffix  -ic 
indicates  a  higher  valence  of  the  element  to  which  it  is 
appended  than  -ous  does. 

Numerical  prefixes  are  sometimes  used  to  indicate  pro- 
portions or  ratios,  as  carbon  monoxide  (CO),  carbon  di- 
oxide (CO2). 

We  have  defined  a  radical  as  a  group  of  elements  that 
seem  to  hold  together  in  most  chemical  reactions.  Many 
of.  these  radicals  have  received  special  names  which  are 
used  as  though  they  were  elements.  The  group  (OH)  is 
known  as  hydroxyl,  (NH4)  as  ammonium,  (CN)  cyano- 
gen. Potassium  hydroxide  (KOH)  and  ammonium  chlo- 
ride (NH4)C1  are  examples  of  compounds  containing 
radicals,  which  follow  the  rule  for  the  naming  of  binary 
compounds. 

115.  Ternary  compounds  contain  three  elements.  The 
name  may  end  in  -ide  provided  all  three  of  the  elements 
are  indicated  in  the  name,  as  sodium  aluminum  fluoride 
(Na8AlF6),  bismuth  oxychloride  (BiOCl). 

It  is  usual,  however,  for  the  names  of  compounds  con- 
taining three  or  more  elements  (or  radicals)  to  end  in  -te 
(ier,  three),  as  potassium  chlorplatinate  (K2PtCl6).  Very 
often  a  third  element  is  not  named ;  in  this  case  it  is  to 
be  understood  that  the  third  element  is  oxygen.  Calcium 
sulphate  (CaSO4)  contains  calcium,  sulphur,  and  oxygen. 

Compounds  whose  names  end  in  -te  are  very  common  in 
the  class  of  compounds  we  have  defined  as  salts;  their 


NAMES  OF  ACIDS  AND   SALTS  111 

names  and  compositions   should  be  associated  with  the 
corresponding  acids. 

116.  Acids  and  Salts.  —  If  the  acid  is  a  binary  compound, 
it  may  be  named  as  such,  hydrogen  chloride.  The  usual 
name  of  the  solution  is  hydrochloric  acid  (HC1).  The 
salts  corresponding  to  these  acids  are  named  as  binary 
compounds  and  have  names  ending  in  -ide,  as  sodium 
chloride. and  lead  sulphide. 

Many  acids  contain  oxygen ;  it  is  not  mentioned  in 
either  the  systematic  or  popular  name.  The  common 
oxygen  acid  of  any  element  uses  the  suffix  -ic.  H2SO4, 
sulphuric  acid,  as  a  ternary  compound  is  hydrogen  sul- 
phate. All  salts  containing  (SO4)  are  sulphates : 
K2SO4  potassium  sulphate,  CaSO4  calcium  sulphate. 

There  are  compounds  having  the  formulas  H2SO3  and 
K2SO3:  these  are  hydrogen  sulphite  or  sulphurous  acid,', 
and  potassium  sulphite.  As  already  stated,  the  suffix  -ic 
indicates  a  higher  oxygen  ratio  than  -ous.  The  compound 
with  name  ending  in  -ate  is  more  highly  oxidized  than 
the  one  ending  in  -ite. 

While  our  system  provides  names  for  several  com- 
pounds of  the  same  elements,  it  by  no  means  follows  that 
such  compounds  exist  or  are  known.  Compounds  whose 
chemical  names  end  in  -ite  are  not  at  all  common. 

Other  designations  are  needed  occasionally,  however. 
The  highest  oxygen  ratio  is  indicated  by  using  the  prefix 
per-  with  the  name  of  the  salt  ending  in  -ate,  or  of  the  acid 
ending  in  -ic.  The  lowest  degree  of  oxidation  is  indicated 
by  the  prefix  hypo-  with  the  name  of  the  salt  ending  in  -ite 
(or  the  -ous  acid). 

Names  and  formulas  should  be  learned  in  connection 
with  the  substances.  The  following  table  will,  however, 
illustrate  the  principles  outlined  above. 


1C- 


112  CHEMICAL  FORMULAS  AND  NAMES 

NAMES  OF  ACIDS  AND  SALTS 


nbiOfj 

Per-chloric  acid 

hydrogen 

KC1O4 

potassium 

perchlorate 

perchlorate 

H/C108 

I 

Chloric  acid 

hydrogen 

KC108 

potassium 

~^      '  N 

chlorate 

chlorate 

HfclOj 

Chlorous  acid 

hydrogen 

KC1O2 

potassium 

v^ 
X-     —   x 

chlorite 

chlorite 

HC1O 

Hypo-chlor-ous  acid 

hydrogen 

KC10 

potassium 

* 

hypochlorite 

hypochlorite 

HC1 

Hydro-chloric  acid 

hydrogen 

KC1 

potassium 

''V"-   ••>-;-     'C 

chloride 

chloride 

It  should  be  borne  in  mind  that  prefixes  and  terminals 
are  essential  parts  of  chemical  names,  to  designate  partic- 
ular compounds,  so  that  chemical  names  cannot  be  abbrevi- 
ated, and  an  error  in  spelling  may  designate  a  different 
compound  from  that  intended.  There  is,  however,  a  tend- 
ency among  chemists  to  simplify  the  spelling  of  a  few 
names,  especially  by  the  omission  of  final  -e,  silent. 


SUMMARY 

NOMENCLATURE    OF    ACIDS    AND    SALTS 

I.  An  acid  is  a  compound  containing  hydrogen,  v^hich  can  be 
replaced  by  a  metal  to  form  a  salt. 

II.  The  name  of  an  acid  ending  in  -ic  is  always  obtained  by 
adding  -ic  to  the  root  derived  from  the  name  of  the  characteristic 
non-metallic  element.     In  each  case  the  formula  for  this  acid 
should  be  committed  to  memory. 

Chlorine  forms  chloric  acid,  HC1O3. 
Nitrogen  forms  nitric  acid,  HNO3. 
Sulphur  forms  sulphuric  acid,  H2S04. 


SUMMARY 


113 


The  acid  containing  one  less  atom  of  oxygen  than  the  -ic  acid 
has  a  name  ending  in  -ous;  e.g.  chlorous  acid,  HC102;  nitrous 
acid,  HNO2;  sulphurous  acid,  H2SO3. 

Acids  containing  less  oxygen  than  the  -ous  acids  have  the  pre- 
fix hypo-  and  end  in  -ous;  e.g.  hypochlorous  acid,  HC1O. 

Acids  containing  no  oxygen  have  the  prefix  hydro-  and  end  in 
ic ;  e.g.  hydrochloric  acid,  HC1. 

These  rules  for  the  names  of  acids  apply  only  to  those  acids 
commonly  classed  among  the  inorganic  compounds. 

III.  Acids  having  the  prefix  hydro-  and  ending  in  -ic  form  salts 
with  names  ending  in  -ide  and  having  no  prefix. 

All  other  acids  with  names  ending  in  -ic  form  salts  with  names 
ending  in  -ate. 

All  acids  whose  names  end  in  -ous  form  salts  whose  names 
end  in  -ite. 


SOME  ACIDS  AND  THEIR  SALTS 


NAME  OF  ACID 

FORMULA 

SALTS  FORMED 

ILLUSTRATIONS  OF  SALTS 

-1.  Hydrochloric  acid 

HC1- 

Chlorides 

NaCl,  sodium  chloride 

2.  Sulphuric  acid     .     . 

H2S04 

Sulphates 

CuSC-4,  copper  sulphate 

3.  Nitric  acid.     .     .     . 

HNOa 

Nitrates 

Pb(NO3)2,  lead  nitrate 

4.  Sulphurous  acid  .     . 

H2S03 

Sulphites 

K2SOs,  potassium  sulphite 

5,  Hydrobromic  acid    . 

HBr 

Bromides 

AgBr,  silver  bromide 

6.  Carbonic  acid      .     . 

HoCOs 

Carbonates 

CaCOa,  calcium  carbonate 

7.  Hydrosulphuric  acid 

H2S 

Sulphides 

ZnS,  zinc  sulphide 

8.  Hydriodic  acid    .     . 

HI 

Iodides 

KI,  potassium  iodide  - 

9.  Nitrous  acid    .     .     . 

H^JO-2 

Nitrites 

NaNO2,  sodium  nitrite 

iO.  Phosphoric  acid  .    .. 

H3P04 

Phosphates 

FePC-4,  iron  phosphate 

1  1  .  Hydrofluoric  acid    . 

HF 

Fluorides 

CaF2,  calcium  fluoride 

12.  Chloric  acid   .     .     . 

HC103 

Chlorates 

KClOs,  potassium  chlorate 

114  CHEMICAL   FORMULAS  AND   NAMES 

EXERCISES 

1.  Define  and  illustrate  (a)  a  symbol ;  (6)  a  chemical  formula. 

2.  State  the  meaning  of  every  symbol  and  figure  in  each 
of  the  following  formulas :    HC1 ;    H2S04;    5C02;    Ca(NO3)2; 
CuS04.5H20. 

3.  How  many  atoms  of  hydrogen  in  each  of  the  following : 
HBr;  H2S04;  NH3;  NH4C2H302;  (NH4)2Fe2(S04)4 .  24  H20  ? 

4.  Making  use  of  the  table  of  atomic  weights  in  the  Appen- 
dix, calculate  the  molecular  weights  of  the  following  com- 
pounds: CuO;  H2S04;  KC103;  ZnCl2;  NaOH. 

5.  Determine  the  vapor  density  of  each  of  the  following 
gases:  02;  03;  H£l ;  C02;  NH*. 

6.  Calculate  Me  weigfit  of  a  liter  of  each  of  the  following 
gases  (standard  conditions):  H2;  OCX;  NH#;  S02;  CO.  . 

7.  Acetylene   gas   has   the    formula   C2H2.     What   is   the 
weight  of  a  liter  of  it  (standard  conditions)  ? 

8.  What  per  cent  of  potassium  chlorate,  KC103,  is  oxygen  ? 

9.  If  a  sample  of  washing  soda  has  a  composition  repre- 
sented by  the  formula  Na-jCOg.  10  H20,  what  per  cent  of  it  is 
water  of  crystallization  ? 

10.  A  hundred  grams  of  a  compound  contain  30.43  grams 
of  nitrogen  and  69.57  grams  of  oxygen.     What  per  cent  of  the 
compound  is  nitrogen  and  what  per  cent  is  oxygen  ?     What 
is  the  ratio  between  the  number  of  nitrogen  atoms  and   the    • 
number  of  oxygen  atoms  ?     What  is  the  simplest  formula  that 
could  be  used  to  express  the  composition  of  the  compound  ? 

11.  A  substance  on  analysis  was  found  to  contain  carbon 
40  %,  hydrogen  6.67  %,  and  oxygen  53.33  %.     What  is  the 
simplest  formula  that  could  be  used  to  represent  such  a  sub- 
stance ? 

12.  Calculate   the   percentage    composition   of   crystallized 
barium  chloride   (BaCl2,  2  H20). 

13.  Calculate  the  percentage  of  water  of  crystallization  in 
crystalline  copper  sulphate,  CuS04 .  5  H20. 

.^.j4''&-i    -i  *  ft*  '>'>&•' A-*-™'  ;;; ; 

/    '  A       «  '  '        .  .  ,        A  <-*  j-      -r-  cJ^  i  • 


EXERCISES 


115 


Calculate  formulas  from  the  following  data : 


NAME 

VAPOR 
DENSITY 

PERCENTAGE  COMPOSITION 

Carbon 

Hydrogen 

14. 
15. 
16. 

17. 

Methane      .... 
Ethane 

8 
15 
22 
29 

75 
80 
81.81 

82.75 

25 

20 
18.18 
17.24 

Propane 

18.  What  weight  of  mercury  could  be  obtained  from  500 
pounds  of  cinnabar,  HgS  ? 

19.  What  weight  of  copper  would  be  obtained  from  250 
grams  of  copper  sulphate,  CuS04  ? 

20.  Calculate  the  empirical  (simplest)  formula  of  a  com- 
pound containing  calcium  29.41  %,  oxygen  47.06  %,  and  sul- 
phur 23.53  %. 

21.  The  vapor  density  of  a  certain  gas  is  14.     What  is  the 
molecular  weight  of  the  gas  ?     It  is  composed  of  carbon  42.8  % 
and  oxygen  57.1  %.     What  is  its  formula? 

22.  Alcohol,  a  liquid  at  ordinary  temperatures,  is  readily 
converted  into  a  gas ;  0.247  gram  of  the  gas  has  a  volume  of 
184.9  c.c.  at  a  temperature  of  150°  C.      What  is  the  vapor 
density  of  the  gas  ?     What  is  the  molecular  weight  of  alcohol  ? 
Alcohol  is  composed  of  carbon  52.2  %,  hydrogen  13.0  %,  oxy- 
gen 34.8  %.     Determine  its  formula. 

23.  0.55  gram  of  a  certain  gas  has  a  volume  of  277.7  c.c.  at 
standard  conditions.     The  gas  is  composed  of  nitrogen  63.6  %, 
oxygen  36.3  %.     What  is  the  formula  of  the  substance  ? 

24.  0.35  gram  of  a  liquid  that  is  easily  vaporized  has,  in  the 
gaseous  form,  a  volume  of  99.7  c.c.  (corrected).     The  substance 
is  composed  of  carbon  92.3  %,  hydrogen  7.7  %.     Determine 
the  formula  of  the  substance. 

25.  Describe  an  experimental  method  of  proving  that  alu- 
minum is  trivalent,  assuming  that  the  atomic  weight  is  known. 


CHAPTER   XIII 
CHEMICAL  EQUATIONS 

117.  Representation  of  Chemical  Reactions  by  Equations. — 

Since  the  symbol  of  an  element  and  the  formula  of  a  com- 
pound represent  more  than  the  name,  we  may  use  them 
instead  of  the  names  in  the  equations  we  have  employed, 
and  then  the  equation  will  represent  definite  masses  as 
taking  part  in  the  reaction. 

These  equations  are  not  algebraic;  they  represent 
changes  that  actually  take  place.  They  cannot,  there- 
fore, be  predicted  with  certainty.  When  we  know  by  ex- 
periment : 

(1)  that  substances  will  react; 

(2)  the  composition  of  each  substance; 

(3)  all  the  products  formed; 

(4)  the  composition  of  each  product, 

we  can  represent  the  reaction  by  an  equation,  and  calcu- 
late the  relative  quantities  involved. 

The  fundamental  principle  upon  which  chemical  calcula- 
tions depend  is  the  indestructibility  of  matter,  so  the 
equation  must  represent  the  same  amount  of  each  element 
after  the  change  as  before.  There  must  be  the  same 
number  of  atoms  of  each  element  represented  on  each  side 
of  the  equation. 

118.  How  an  Equation  is  Written.  —  The   reacting   sub- 
stances are  usually  written  first,  on  the  left;  the  products 

116 


BALANCING   OF  EQUATIONS  117 

on  the  right;  the  arrow  (or  the  equality  sign)  is  not  to  be 
read  "equal  to,"  but  yield  or  form;  the  addition  sign 
with.  As  the  change  may  occur  under  different  conditions, 
no  attempt  is  made  to  represent  how  the  action  occurred. 
In  order  to  show  how  an  equation  is  balanced,  the 
equation  for  the  decomposition  of  potassium  chlorate  will 
be  taken  up  in  detail.  On  heating  potassium  chlorate, 
two  products  result,  potassium  chloride  and  oxygen. 
Potassium  chlorate  has  the  composition  shown  by  the 
formula  KC1O3;  potassium  chloride,  KC1;  and  we  have 
shown  (§  97)  that  there  are  two  atoms  in  the  molecule  of 
oxygen,  O2.  Using  these  formulas,  we  have:  KC1O3 — *- 
KC1  +  O2;  but  it  will  be  seen  that  there  are  three  atoms 
of  oxygen  on  the  left  and  only  two  on  the  right-hand  side 
of  the  equation.  An  equal  number  of  atoms,  however, 
must  appear  on  each  side.  In  order  that  the  quantities  and 
compositions  shall  be  correctly  represented,  it  is  necessary 
that  suitable  coefficients  be  supplied,  so  that  the  equation 
will  balance.  The  equation  will  then  read: 

2KC103— ^2KC1  +  302 

In  this  equation,  we  have  on  each  side  2  atoms  of  potas- 
sium, 2  of  chlorine,  and  6  of  oxygen. 

Materials  which  are  present,  but  which  undergo  no 
change,  such  as  water  in  which  the  substances  are  dis- 
solved, catalytic  agents,  etc.,  are  not  expressed  in  the 
equation. 

119.  Equations  for  Reactions  already  Studied.  —  In  the 
sections  which  follow,  the  equations  for  the  chemical 
changes  already  studied  are  correctly  given.  In  order  to 
master  these,  the  following  method  is  recommended: 

During  the  study  of  this  chapter,  the  student  should 
constantly  review  the  reactions  which  the  equations  repre- 


118  CHEMICAL   EQUATIONS 

sent.  He  should  turn  back  to  the  word  equations  already 
given  where  the  reactions  were  originally  described,  if  the 
heading  of  the  paragraph  does  not  recall  the  equations  to 
his  mind.  The  word  equation  for  each  reaction  should 
next  be  written,  the  formula  for  each  compound  placed 
beneath  its  name,  and  the  equation  balanced  without 
reference  to  the  text.  The  final  equation  should  then  be 
verified.  Each  important  equation  in  the  succeeding 
chapters  should  be  studied  in  the  same  way. 

120.  Oxides  and  Oxygen.  —  The  heating  of  carbon,  sul- 
phur, and  iron  in  the  air  results  in  the  formation  of  an 
oxide  of  the  element  heated  in  each  case  (§  25).  The 
equations  are  : 

C+     O2^CO2   L-- 
S+    O2^SO2     ^ 

3Fe  +  2O2—  ^Fe3O4 

i 

The  slow  oxidation  of  phosphorus,  made  use  of  in  the 
analysis  of  air,  and  the  burning  of  phosphorus  in  oxygen 
(Fig.  10)  are  both  represented  by  the  equation  : 


Thus  we  find  that  the  product,  phosphorus  pentoxide, 
is  the  same  whether  the  phosphorus  combines  with  the 
oxygen  slowly  and  quietly,  or  rapidly  and  violently.  All 
the  above  equations  illustrate  the  process  of  direct  combi- 
nation, or  synthesis. 

The  production  of  oxygen  from  mercuric  oxide  and 
from  potassium  chlorate  illustrates  the  opposite  process, 
simple  decomposition,  or  analysis.  The  equations  are  : 


2HgO    -^2Hg  +0 
2KC10—  *- 


THE  FORMATION  OF   WATER  119 

121.    Hydrogen.  —  The  equation  for  the  preparation  of 
hydrogen  by  electrolysis  of  water  (§  33)  is  : 

2H2O—  -^2H2  +  O2 

When  sodium  reacts  on  water,  we  have  : 

2  Na  +  2  H2O—  *-2  NaOH  +  H2 

For  the  formation  of  hydrogen  by  the  reaction  between 
metals  and  acids,  we  have  the  following  equations  : 


Zn  +H2SO4  — 

Mg  +  2  HC1  —  >-  MgCl2  +  H2 

/ 

The  formulas  of  sulphuric  acid  and  zinc  sulphate  show 
very  clearly  how  the  latter  is  produced  by  the  replacement 
of  the  hydrogen  of  the  acid  by  the  zinc.  The  formation 
of  sodium  hydroxide  and  magnesium  chloride  in  the  equa- 
tions given  above  furnish  other  examples  of  simple  replace- 
ment. 

122.  The  Formation  of  Water  by  the  burning  of  hydrogen 
in  oxygen  or  in  air  (§  37)  is  represented  by  the  equation  : 

2H2  +  02—  ^2H20 

It  will  be  noticed  that  this  is  the  exact  reverse  of  the 
equation  given  above  for  the  decomposition  of  water.  A 
large  proportion  of  our  equations  are  reversible;  that  is, 
the  direction  in  which  the  reaction  proceeds  depends  upon 
the  conditions.  This  may  be  shown  by  the  use  of  the 
double  arrow  ,  so  we  may  write  the  equation  : 


The  reduction  of  copper  oxide  by  hydrogen  (§  38)  is 
expressed  by  the  equation  : 


120  CHEMICAL  EQUATIONS 

Hydrogen  has  a  great  tendency  to  unite  with  oxygen,  and 
so  takes  this  element  away  from  the  copper. 

123.  Preparation    of    Chlorine   by   electrolysis   of   brine 
(§  74)  is  represented  by  the  equation  : 

2  NaCl  +  2  H20  — >-  2  NaOH  +  H2  +  Cla 

This  equation  represents  the  final  result  of  the  reaction, 
and  does  not  show  the  intermediate  steps ;  viz.  the  separa- 
tion of  the  sodium  and  chlorine,  and  the  reaction  of  the 
former  with  the  water  to  form  sodium  hydroxide. 

The  liberation  of  chlorine  by  the  oxidation  of  hydro- 
L  chloric  acid  in  the  presence  of  a  catalytic  agent  (§  75)  is 
represented  by  the  equation  : 

4  HC1  +  02  — ^  2  H20  +  2  C12 

When  manganese  dioxide  is  used  as  the  oxidizing  agent, 
the  equations  are : 

MnO2  +  4  HC1  — >-  MnCl2  +  2  H2O  +  Cla 

Mn02  +  2  NaCl  +  2  H2SO4  — >-  MnSO4  +  Na2SO4 

+  2  H20  +  C12 

A  comparison  of  these  three  equations  shows  the  forma- 
tion of  water  and  chlorine  in  each  case.  We  shall  see 
from  the  equation  for  the  formation  of  hydrochloric  acid- 
given  below  that  in  all  three  methods  we  may  regard  the 
liberation  of  the  chlorine  as  the  result  of  the  oxidation  of 
the  hydrogen  of  hydrochloric  acid.  One  atom  of  oxygen 
in  the  manganese  dioxide  oxidizes  two  molecules  of  hydro- 
chloric acid. 

124.  Chlorides. —  The  following  equations  represent  the 
reaction  of  chlorine  with  various  substances,  resulting  in 
the  formation  of  chlorides  (§§  77-79)  : 


TEST  FOR  A    CHLORIDE  121 

H 


2       -j     — 
2Sb  +  3Cl2—  ^2SbCl3 
Zn     +C12    _ 
H20  +  C12    — 

The  last  equation  represents  the  liberation  of  nascent 
oxygen,  in  the  bleaching  by  chlorine,  so  we  write  the 
symbol  O,  indicating  the  oxygen  atom,  and  not  O2,  indicat- 
ing the  oxygen  molecule.  It  will  be  seen  that  this 
equation  is  the  reverse  of  that  given  above  for  the  prepa- 
ration of  chlorine,  except  that  in  that  case  the  oxygen  is 
not  represented  as  nascent,  but  as  ordinary  oxygen,  and 
the  equation  is  balanced  accordingly. 

125.  Hydrochloric  Acid.  —  Two   methods   for   producing 
hydrochloric  acid  are  indicated  in  the  equations  just  given. 
We  may  represent  its  formation  from  salt  and  sulphuric 
acid  (§  82)  as  follows  : 

2  NaCl  +  H2SO4  —  >-  Na2SO4  +  2  HC1 

This  equation  illustrates  double  replacement  or  metathesis, 
more  often  called  double  decomposition  ;  each  compound 
apparently  breaks  up  into  two  parts,  each  of  which  unites 
with  a  different  part  of  the  other  compound.  Such  reac- 
tions can  only  be  prevented  from  becoming  reversible  by 
the  removal  of  one  of  the  products  from  the  field  of 
action  ;  in  this  case  hydrogen  chloride  is  driven  off  as  a 
gas.  Double  replacements  are  common  in  solutions. 

126.  Test  for  a  Chloride.  —  As  a  typical  reaction   illus- 
trating this  test,  we   may  take  the  reaction  of   sodium 
chloride  with  silver  nitrate  (§  88)  : 

t  ~  J.     -  4  -  -4      - 

NaCl  +  AgNO3  —  ->-  AgCl  +  NaNO8 


122  CHEMICAL  EQUATIONS 

The  products  of  the  double  replacement  in  this  case  are 
silver  chloride  and  sodium  nitrate.  This  reaction  is  pre- 
vented from  becoming  reversible  by  the  fact  that  silver 
chloride,  being  insoluble,  is  precipitated,  and  so  is  removed 
from  the  field  of  action  as  rapidly  as  it  is  formed. 

SUMMARY 

Chemical  reactions  are  represented  by  equations  in  which  the  re- 
acting substances  are  written  on  the  left  and  the  products  on  the 
right,  separated  by  an  equality  sign  or  an  arrow. 

Equations  represent  actual  chemical  changes  and  must  repre- 
sent the  same  amount  of  each  element  after  the  change  as  before. 
The  composition  of  each  reacting  substance  and  of  all  the  prod- 
ucts must  be  known  before  .  the  equations  can  be  written. 
Catalytic  agents,  and  solvents  that  are  unaffected  are  not  ex- 
pressed in  the  equation.  The  conditions  of  the  chemical  action 
are  not  indicated  by  the  equation. 

Equations  may  represent  processes  of : 

(a)  direct  combination  ;  (d)  double  replacement ; 

(b)  decomposition  ;  (e)  oxidation  and  reduction. 

(c)  simple  replacement ; 

A  reversible  reaction  is  one  in  which  the  reaction  may  proceed 
in  either  direction  according  to  conditions.  A  reaction  will  not 
be  reversible  if  one  of  the  products  is  eliminated  as  a  gas  or  as 
an  insoluble  substance  during  the  reaction. 

EXERCISES 

1.  Write  an  equation  for  (a)  a  synthesis,  (6)  an  analysis. 

2.  Distinguish  between  analysis  and  synthesis. 

3.  Write  the  equation  for  the  reaction  that  takes  place  when 
potassium,  a  metal  similar  to  sodium,  reacts  with  water.     What 
process  does  the  equation  represent  ? 


EXERCISES  123 

4.  Write   a  reversible  equation    involving  hydrogen  and 
chlorine.     Tell  how  you  can  control  the  direction  in  which  the 
action  proceeds. 

5.  Write  the  equation  for  the  reaction  that  might  reason- 
ably be   expected   to   occur   if   sodium   chlorate,   NaClO3,   is 
heated. 

6.  Write  the  equation  for  the  reaction  of  potassium  chlo- 
ride, KC1,  with  sulphuric  acid.     Name  the  process  and  the 
products.     Explain  why  the  reaction  is  not  ordinarily  revers- 
ible. 

7.  Distinguish  between  simple  replacement  and  double  re- 
placement. 

8.  Write  the  equation  for  a  laboratory  preparation  of  chlo- 
rine. 

9.  Write  the  equation  expressing  the  reaction  of  magne- 
sium with  oxygen ;  with  sulphuric  acid ;   with  chlorine ;   and 
with  hydrochloric  acid. 

Name  the  products  and  the  process  illustrated  in  each  case. 

10.  Explain  what  is  meant  by  double  replacement  and  illus- 
trate it  by  an  equation. 

11.  Complete  and  balance  the  following  equations,  using 
formulas  throughout : 

/  manganese  dioxide  +  hydrochloric  acid  — >- 
I/  hydrogen  +  hot  copper  oxide  — >- 
/  phosphorus  +  oxygen  — >- 
calcium  -f  hydrochloric  acid — *- 

i    12.   Express  the  following  in  symbols  and  formulas   and 
complete  the  chemical  equations  : 

V(a)   the  action  of  dilute  sulphuric  acid  on  zinc  ; 

V  (6)   the  reaction  between  silver  nitrate  and  barium  chloride. 

J      13.    Write  an  equation  representing  zinc  as  taking  part  in  a 
synthesis.     In  a  simple  replacement. 


124  CHEMICAL  EQUATIONS 

14.    What  types  of  chemical  change  are  represented  by  each 
of  the  following  : 


2  K  +  2  H20  —  >-2  KOH  +  H 


2  NaOH  +  H2S04  —  >-  Na,S04  +  2  H2O 

Mg(OH)2—  ^MgO  +  H20 
Fe304  +  4  H2^±I3  Fe  +  4  H2O 

1    15.    Write   the    equation   for   the   reaction    between   silver 
nitrate  and  barium  chloride,  BaCl2. 

4    16.   Tin   dioxide,   Sn02,  is  formed   by  heating   tin  in  air. 
^  Write  the  equation. 

H     17.    Write  the  equation  for  the  reaction  in  the  oxy-hydrogen 
blowpipe. 

^18.    Write  the  equations  for  :    - 

(a)  potassium  taking  part  in  a  simple  replacement. 

(6)  the  potassium  in  the  compound  formed  participating 

in  a  double  replacement. 
M 

19.    Write  the  reversible  equation  for  the  actions  by  which 

Lavoisier  proved  what  happened  when  a  metal  was  heated  in 
air. 

\    20.   Write    the    equation    showing   the    formation    of   zinc 
chloride,  ZnCl2,  from  zinc. 


CHAPTER   XIV 

CHEMICAL  CALCULATIONS 

THE  calculations  from  chemical  equations  may  be 
divided  into  three  classes  :  those  involving  weight  only, 
those  involving  volume  only,  and  those  involving  both 
weight  and  volume.  Each  type  of  problem  will  be  sepa- 
rately discussed. 

127.  Calculation  of  Eelative  Weights  from  the  Equation.  — 
In  the  equation 

2KC10  —  ^ 


the  molecule  of  potassium  chlorate  weighs 
39  +  35.5  +  3x16(122.5); 

the  molecule  of  potassium  chloride  weighs 
39  +  35.5  (74.5); 

the  oxygen  molecule  weighs 

2  x  16  (32). 

v 

That  is,  2  x  122.5,  or  245  parts  by  weight  of  potassium 
chlorate,  on  being  decomposed,  give  2  x  74.5  (149)  parts 
of  potassium  chloride,  and  3  x  32  (96)  parts  of  oxygen. 

2KC1O3  —  >-  2KC1         +        3O2 

2  x  122.5         2  x  74.5  3  x  32 

245  149  96 

Now  the  same  relation  exists  between  the  actual  weights  ex- 
pressed in  grams,  pounds,  tons,  etc.,  as  exists  between  the 
chemical  weights  represented  by  the  equation. 

125 


126  CHEMICAL   CALCULATIONS 

Suppose  we  wish  to  prepare  20  grams  of  oxygen ;  how 
much  potassium  chlorate  must  be  used  ?  The  numbers 
we  have  calculated  from  the  equation  show  that  245  grams 
of  potassium  chlorate  produce  96  grams  of  oxygen,  or,  in 
other  words,  that  the  weight  of  potassium  chlorate  is  about 
2|-  times  that  of  the  oxygen  evolved.  It  appears,  there- 
fore, that  we  shall  need  about  50  grams  of  potassium  chlo- 
rate to  obtain  20  grams  of  oxygen.  The  exact  number 
can  be  obtained  from  the  proportion : 

96  :  245  : :  20  grams  :  x  grams 

96^  =  4900 
x  —  51.0  grams,  the  potassium  chlorate  needed 

This  answer  agrees  with  the  result  of  our  previous  mental 
calculation.  It  is  well  to  thus  make  a  preliminary  mental 
approximation  in  every  case  before  stating  the  arithmetical 
proportion. 

What  quantity  of  sulphuric  acid  (H2SO4)  is  needed  to 
exactly  decompose  100  grams  of  sodium  chloride,  when 
sodium  sulphate  and  hydrogen  chloride  are  formed  ? 

The  solution  of  the  problem  may  be  briefly  stated  as 
follows : 

100  grams  x  grams 

2NaCl  +    H2SO4    — >-    Na2SO4  +  2  HC1 

117  98 

Na-23  H2=    2 

Cl  =  35.5  S    =  32 

58.5x2  =  117  O4=64 

98     . 

117  :  98  : :  100  grams  :  x  grams 
x=  83.8  grams,  sulphuric  acid  required 

It  will  be  noticed  that  only  the  reacting  weights  of  the 
two  substances  involved  in  this  particular  problem,  one 


RELATIVE    WEIGHTS  FROM  THE  EQUATION    127 

' 
whose  weight  is  given  and  one  whose  weight  we  wish  to 

find,  have  been  used. 

Similarly,  and  as  though  it  were  a  new  problem,  the 
weight  of  the  sodium  sulphate  might  be  found : 

100  grams  x  grams 

2NaCl  +   H2S04  ~>-     Na^    +    2HC1 

117  142 

Na  =  23  Na2=    46 

Cl  =35.5  S      =    32 

58.5x2  =  117  Q4   =    64 

142 

117  :  142  : :  100  grams  :  x  grams 
x  =  121.3  grains,  sodium  sulphate  produced 

By  the  same  method  we  may  find  the  weight  of  the 
hydrogen  chloride : 

100  grams  x  grams 

2NaCl  +   H2SO4  — ^  Na2SO4  +   2  HC1 
117  73 

Na  =  23  H  =  1 

Cl  =35.5  Cl  =  35.5 

58.5x2  =  117  36.5x2  =  73 

117  :  73  : :  100  grams  :  x  grams 
x—  62.4  grams,  hydrogen  chloride  produced 

128.   Calculation  of  Relative  Volumes  from  the  Equation.  — 

The  method  in  the  preceding  paragraphs  applies  to  the 
weights  of  all  substances,  solid,  liquid,  or  gaseous.  But  in 
the  case  of  gases,  we  found  the  formula  has  a  meaning 
that  did  not  apply  to  liquids  or  solids  (cf.  §  106). 

Problems  involving  volume  only  are  simple  to  solve,  be- 
cause the  relation  between  the  numbers  of  molecules  of  the 


128  CHEMICAL   CALCULATIONS 

gases  represented  in  the  chemical  equation  is  the  same  as  that 
between  the  volumes  of  these  gases  (§  96). 
In  the  equation 

2  H2  +  02  —  >-  2  H20 

it  appears  that  two  molecules  of  hydrogen  react  with 
one  molecule  of  oxygen  to  form  two  molecules  of  steam. 
Since  equal  numbers  of  molecules  occupy  equal  volumes, 
the  volume  of  the  hydrogen  must  be  twice  that  of  the 
oxygen  and  equal  to  that  of  steam. 
In  the  equation  : 

2  H2O  +  2  C12  —  >-  4  HC1  +  O2 

we  see  that  two  molecules  of  chlorine  are  used  to  liberate 
one  molecule  of  oxygen,  hence  two  volumes  of  chlorine 
will  furnish  one  volume  of  oxygen.  Therefore,  in  the 
case  of  gases,  the  coefficients  represent  the  relative  volumes 
of  the  substances. 
The  equation 

H  +  C1—  ^ 


may  be  read  :  1  part  by  volume  of  hydrogen  with  1  part 
by  volume  of  chlorine  will  give  2  parts  by  volume  of  hy- 
drogen chloride  ;  and  also  2  parts  by  weight  of  hydrogen 
and  71  parts  by  weight  of  chlorine  give  73  parts  by  weight 
of  hydrogen  chloride. 

Suppose  that  we  are  required  to  calculate  how  many 
liters  of  oxygen  would  be  liberated  by  the  complete  re- 
action of  12  liters  of  chlorine  with  water.  The  problem 
and  its  solution  may  be  stated  as  follows  : 

12  liters  x  liters 

2H2O      +     2C12     —  *-     4HC1     +      O2 

2  vol.  1  vol. 

2  :  1  :  :  12  liters  :  x  liters. 
x  =  6  liters,  volume  of  oxygen  liberated. 


PROBLEMS   OF    WEIGHT  AND    VOLUME         129 

129.  Problems  involving  Both  Weight  and  Volume  include 
cases  in  which  the  object  is  to  determine  the  weight  of  a 
certain  compound  required  for  the  production  of  a  given 
volume  of  a  gas,  or  vice  versa.  Two  methods  for  the  solu- 
tion of  this  type  of  problem  are  given  in  this  and  the 
following  sections.  The  method  to  be  employed  by 
a  particular  class  of  students  will  be  determined  by 
the  method  already  selected  for  the  determination  of 
molecular  weights  (§§  101,  102). 

The  first  method  is  shown  by  the  solution  of  the  fol- 
lowing problems : 

How  many  liters  of  a  gas  can  be  obtained  by  heating  20 
grams  of  mercuric  oxide  f  First,  write  the  equation  and 
calculate  the  number  of  grams  of  oxygen  by  the  method 
given  in  §  127. 

20  grams  x  grams 

2HgO     -^  2Hg     +      02 

432  32 

Hg  =  200  O2  =  32 

O  =  16 

216  x  2  =  432 

432  :  32  : :  20  grams  :  x  grams 
x  =  1.48  grams  oxygen. 

But  the  problem  asks  for  the  number  of  liters  of  oxy- 
gen. 

We  can  always  find  the  approximate  weight  of  1  liter 
of  a  gas  from  the  molecular  weight  (§  101)  : 

%2-  =  16,  V.D.  of  oxygen.     .-.  1  liter  of  oxygen  weighs  - 
16  x  0.09  =  1.44  grams.     Hence 

-1—  =  1.027  liters,  oxygen  produced. 


130  CHEMICAL   CALCULATIONS 

How  many  grams  of  potassium  chlorate  must  be  heated  to 
obtain  10  liters  of  oxygen  ? 

In  this  type  of  problem,  as  we  have  not  the  real  weight 
given,  we  must  calculate  it  from  the  number  of  liters 
given.  The  first  step  in  the  problem  is  to  find  the  weight 
of  the  given  volume  of  oxygen.  The  second  step  is  a 
problem  of  the  usual  type,  with  one  weight  given,  to  find 
the  other.  The  two  steps  are  given  in  detail  below. 

(I)  3f.=  16,  V.D.  of  oxygen. 

.-.  1  liter  of  oxygen  weighs  16  x  0.09  =  1.44  grams. 
10  x  1.44  =  14.4  grams,  weight  of  oxygen. 

(II)  x  grams  14.4  grams 
2KC1O3             -^   2KC1    +  3O2 

245  96 

K  =  39  O2  =_32 
Cl  =  35.5  32  x  3  =  96 

03  =  48_ 


122.5x2  =  245 

245  :  96  : :  x  grams  :  14.4  grams 
x  =  36.8  grams,  potassium  chlorate  required. 

130.  Problems  involving  Both  Weight  and  Volume :  Direct 
Method.  —  The  volume  of  gases  reacting  can  be  directly 
calculated  from  the  equation,  if  we  keep  in  mind  the  fol- 
lowing fact  (§  102) :  when  weights  are  expressed  in 
grams,  every  gram-molecule  of  gas  represented  by  the 
equation  stands  for  22.^  liters.  From  the  relations  be- 
tween the  units  it  is  also  true  that,  when  weights  are  ex- 
pressed in  kilograms,  every  kilogram-molecule  of  the  gas 
stands  for  22.^  cubic  meters;  and  when  weights  are  ex- 
pressed in  ounces  (Avoirdupois),  each  ounce-molecule  of 
gas  stands  for  22.  S  cubic  feet. 


PROBLEMS   OF   WEIGHT  AND    VOLUME         131 

Suppose  we  wish  to  produce  50  liters  of  hydrogen  by 
the  reaction  : 

Zn  +  H2SO4  — >-  ZnSO4  +  H2 

65  grams  of  zinc  give  2  grams  of  hydrogen.  But  2  grams 
of  hydrogen  is  a  gram-molecule  of  hydrogen,  and  occupies 
22.2  liters.  Hence  65  grams  of  zinc  give  22.2  liters  of 
hydrogen.  The  problem  may  then  be  stated  as  follows : 

x  grams  50  liters 

Zn       +H2S04— ^ZnS04+        H2 
65  grams  22.2  liters 

Zn  =  65  H2  =  1  molecule  of  hydrogen 

and  in   this   problem  stands 

for  22.^f  liters 

*  22.2  liters  :  50  liters  : :  65  grams :  x  grams 

x  =  146.4  grams,  zinc  needed. 
In  the  decomposition  of  potassium  chlorate : 
2  KC1O3  — >-  2  KC1  +  3  O2 

only  one  of  the  substances  is  gaseous ;  245  grams  of 
potassium  chlorate  give  3  gram  molecules  of  oxygen 
(3  O2),  which  occupy  3  x  22.3  liters.  If  we  wish  to  pro- 
duce 100  liters  of  oxygen,  we  can  find  the  weight  of 
potassium  chlorate  needed,  by  the  following  solution : 

x  grams  100  liters 

2KC1O3  — >-    2KC1    +              3O2 

245  3  x  22.2  liters 

K  =39  3  x  22.2  =  66.6 

Cl  =  35.5 

03  =  48_ 


122.5x2  =  245 

66.6  liters  :  100  liters  ::  245  grams  :  x 
x  =  367.9  grams,  potassium  chlorate  needed. 


132  CHEMICAL   CALCULATIONS 


SUMMARY 

The  relative  weights  of  the  different  substances  in  a  chemical 
equation  can  be  calculated.  Such  calculations  deal  with  but  two 
of  the  substances  at  a  time.  The  weights  of  the  substances  are 
in  the  same  ratio  as  the  weights  of  the  molecules  involved.  With 
the  weight  in  grams  of  one  of  the  substances  known,  and  the 
weights  of  the  molecules  ascertained,  a  proportion  is  formed  with 
these  three  quantities.  The  weight  in  grams  of  the  second  sub- 
stance is  found  by  solving  the  proportion. 

Relative  volumes  of  gaseous  substances  are  represented  by  the 
coefficients  of  their  molecules  in  an  equation. 

Problems  involving  weight  and  volume  may  be  solved  by  finding 
the  weight  of  the  gas  involved  and  then  forming  a  proportion  in- 
cluding the  3  known  quantities  and  the  unknown  quantity.  It  is 
sometimes  convenient  to  make  use  of  the  fact  that,  when  weights 
are  expressed  in  grams,  each  molecule  of  the  gas  represented  in 
the  chemical  equation  stands  for  22.$  liters. 

EXERCISES 

\    t 

1.  Calculate  the  weight  of  oxygen  obtained  from  heating 
36  grams  of  mercury  oxide. 

2.  How  many  grams  of  copper  were  heated  to  form  2.64 
grams  of  copper  oxide  ?  f  ~^'iSL  '.  /$  y  ^ 

3.  2.4  grams  of  zinc  were  treated  with  an  excess  of  dilute 
sulphuric  acid.     Calculate  weight  of  each  product  forme(J. 
'•'.*Sv    .:   -'  »fy-/4/   .".  tvl'p*    ^,f     '. /*7  .y- 

4?  Find  how  many  grams  (a)  of  potassium  chloride,  KC1, 

and  (6)  of  sulphuric  acid  are  needed  to  produce  2.8  grams  of 
hydrogen  chloride. 

5.  Calculate  the  weight  of  manganese  dioxide  and  that  of 
hydrogen  chloride  used  to  produce  4.8  grams  of  chlorine. 
How  many  grains  of  manganese  chloride  were  formed?  £.5 


z*        **•  -%.'**-— 

Hi  fr  .'  Va  So^:  y%M   :  ^  ^  '*          /. 

/if  i.  EXERCISES  133 

6.  How   much   sodium  chloride,  reacting  with   sulphuric   / 
acid,  would  be  necessary  to  produce  10  grams  of  dry  sodium 
sulphate?    fc  /  ^->  f\ft^  ty 

7.  An  experiment  showed  that,  when  2.16  grams  of  silver 
were  treated  with  chlorine,  2.87  grams  of  silver  chloride  were 
formed.    Calculate  from  this  result  the  atomic  weight  of  silver. 

8.  How  much   zinc  is  required  to  prepare  10  grams  of 
crystallized  zinc  sulphate,  ZnS04 .  7  H20  ? 

9.  What  weight  of  oxygen  is  required  to  unite  with  21 
grams  of  iron  to  give  the  magnetic  oxide  of  iron,  Fe304  ?   Whatv- 
volume  will  this  oxygen  occupy  at  10°  C.  and  750  mm.  ? 

10.  State  the  relative  volumes  of  each  gaseous  substance  in- 
dicated by  the  equations  representing : 

(a)  hydrogen  combining  with  chlorine ;  // 

(b)  chlorine  combining  with  water ; 

(c)  hydrogen  combining  with  bromine  >""//  ^t  / 

(d)  electrolysis  of  sodium  chloride. 

11.  30  c.c.  of  hydrogen  \TQ  mixed  with  40  c.c.  of  air  that 
contains  20  %  of  oxygen,  and  the  mixture  is  ignited.     What 
gases  remain  after  explosion  and  what  is  the  volume  of  each  ? 
All   gas   volumes   in  this   question  are   to  be  considered  at 
standard  conditions,  jjfr  /•  t£--0*  "-y. 

12.  How  many  volumes  of  oxygen  are  required  to  burn  one 
volume  of  methane  (CH4)  to  carbon  dioxide  and  water  ? 

13.  How  many  liters  of  oxygen  at  standard  conditions  can  .  . 
be  obtained  by  heating  8.4  grams  of  potassium  chlorate  ? 

14.  How  many  liters  of  oxygen  at  standard  conditions  would 

be  formed  by  the  complete  decomposition  of  25  grams  of  mer-      /  i 
curie  oxide  ? 

15.  What  volume   of   oxygen,   under  standard  conditions, 
could  be  obtained  by  the  electrolytic  decomposition  of  2  grams 
of  water  ? 

x4^  ->  AM-  *4.  ,, 

0^  t-r  t-r    -•  .  /    a     -     /.£ 


134  CHEMICAL   CALCULATIONS 

16.  What  volume  of   hydrogen  measured  under  standard 
conditions  is  required  to  reduce  11.94  grams  of  copper  oxide  ? 
What  is  the  weight  and  what  is  the  volume  of  the  liquid 
(water)  formed  ? 

17.  How  many  grams  of  zinc  sulphate  would  be  formed 
during  the  production  of  250  liters  of  hydrogen  by  the  reaction 
between  zinc  and  diluted  sulphuric  acid  ? 

18.  How  many  grams  of  potassium  chlorate  would  be  re- 
quired for  the  preparation  of  10  liters  of  oxygen  at  standard 
conditions  ? 

19.  How  many  grams  of  mercuric  oxide  are  required  for  the 
preparation  of  8  liters  of  oxygen  under  standard  conditions  ? 

20.  How  many  grams  of  zinc  are  necessary  for  the  produc- 
tion of  90  liters  of  hydrogen  measured  under  standard  con- 
ditions, by  the  action  of  hydrochloric  acid  on  the  metal  ? 

21.  How  many  grams  of  sodium  chloride  would  be  required 
for  the  preparation  by  electrolysis  of  29.4  liters  of  chlorine 
at  750  mm.  and  21°  C  ? 

22.  How  many  kilograms  of  iron  would  be  required  to  fur- 
nish hydrogen  enough  to  fill  a  balloon  of  6350  cubic  meters 
capacity  ? 

Fe  +  H2S04  — >-  FeS04  +  H2 


2.1 


CHAPTER  XV 
T    m^  SODIUM  AND  POTASSIUM   ft*    T 

131.  Preparation  of  Sodium.  —  The  great  chemical  activ- 
ity of  sodium  and  the  stability  of  its  compounds  made 
the  preparation   of  metallic  sodium  a  difficult   chemical 
problem.    Like  many  others,  it  was  solved  by  the  application 
of   electricity.      Sir  Humphry 
Davy,  in  1807,  obtained  both 
sodium  and   potassium  by  the 
electrolysis  of  the  melted  hy- 
droxides,  and   the   metals  are 
now  prepared  commercially  by 
this  method  (Fig.  36). 

The  sodium  hydroxide  is  con- 
tained in  an  iron  pot,  in  which 
it  is  melted.  The  cathode  is 
an  iron  rod  coming  up  through 
the  bottom  of  the  cylinder. 
The  anode  is  an  iron  or  nickel 
cylinder  coming  down  from  the 
top  and  surrounding  the  cath- 
ode. A  metal  cylinder  with 
removable  cover  is  suspended 
so  as  to  come  down  inside  the  anode  cylinder. 

When  the  current  is  passed  through  the  melted  hydrox-  / 
ide,  the  sodium  and  hydrogen  appear  at  the  cathode  and 
the    oxygen    at  the  anode.       Suspended  from   the  metal 
cylinder  is  a  cylinder  of  wire  gauze  (<?,  c)  through  which 

136 


FIG.  36. 


136  SODIUM  AND  POTASSIUM 

the  fused  hydroxide  (a)  can  pass,  but  which  prevents  the 
passage  of  bubbles  of  the  gas  or  globules  of  melted  sodium. 
The  molten  sodium,  being  lighter  than  the  melted  hy- 
droxide, rises  to  the  surface  (5)  above  the  cathode,  and 
is  ladled  off  from  time  to  time.  The  hydrogen  escapes 
through  holes  in  the  cover  and  the  oxygen  is  led  off 
through  a  pipe  from  the  side.  The  reasons  for  these 
precautions  will  be  readily  understood  when  we  keep  in 
mind  the  energy  with  which  oxygen  combines  with  both 
sodium  and  hydrogen.  The  heat  generated  by  the  passage 
of  the  current  is  sufficient  to  keep  the  hydroxide  molten 
after  the  action  starts.  The  equation  for  the  electrolysis  is  : 

-^  2  Na  +  O   +  H 


132.  Physical  Properties  of  Sodium.  —  Sodium  is  a  silver- 
white  metal,  possessing  a  brilliant  luster  when  in  a  pure 
state.     It  is  soft  enough  at  ordinary  temperatures  to  be 
readily  cut  with  a  knife  and  to  be  molded  by  the  fingers. 
It  may  be  formed  into  wire  by  pressing  it  through  a  hole 
in  a  metal  plate.     It  is  a  very  light  metal,  slightly  less 
dense  than  water.     It  is  a  good  conductor  of  heat  and  of 
electricity.     Other  properties  of  sodium,  however,  prevent 
its  practical  use  as  an  electric  conductor.      "  Metallic  " 
luster  and  conductivity  of  heat  and  electricity  are  char- 
acteristic physical  properties  of  metals. 

133.  Chemical  Activity.  —  Sodium  is  in  general  a  very 
active  element  chemically.      It  burns  readily  in  oxygen 
and  in  chlorine,  and  is  an  energetic  reducing  agent.     The 
color  of  its  flame  is  bright  yellow,  and  this  color  is  im- 
parted to  a  non-luminous  flame  when  any  sodium  com- 
pound is  heated  in  it. 

134.  Action  with  Water.  —  The  most  striking   chemical 
property  of  sodium  is  its  action  with  water.     Exposed  to 


Sir  Humphry  Davy  (1778-1829)  was  the  most  brilliant  of  Eng- 
lish investigators.  He  early  appreciated  the  value  of  the  atomic 
theory  and  adopted  it.  He  discovered  the  anesthetic  properties  of 
nitrous  oxide.  He  made  a  very  extended  study  of  the  effect  of 
passing  an  electric  current  through  substances  and  solutions,  dis- 
covering by  this  means  several  new  elements,  notably  sodium  and 
potassium. 

Davy  explained  the  chemical  nature  of  acids  as  compounds  of 
hydrogen,  a  view  not  hitherto  held.  He  announced  chlorine  as 
an  element.  He  is  famed  as  the  inventor  of  the  miner's  safety 
lamp. 

For  seven  years  he  was  president  of  the  Royal  Society  of  England. 


ACTION  WITH   WATER  131 

moist  air,  it  tarnishes  almost  instantly  on  account  of  the 
formation  of  a  layer  of  sodium  hydroxide.  In  perfectly 
dry  air,  it  remains  unchanged  at  ordinary  temperatures. 
When  thrown  on  water,  it  skims  over  the  surface  with  a 
hissing  sound  (§  34).  The  water  is  rapidly  decomposed, 
one  half  the  hydrogen  being  set  free,  and  the  sodium  com- 
bines with  the  oxygen  and  the  other  half  of  the  hydrogen 
to  form  sodium  hydroxide  : 

2  Na  +  2  H2O  — >  2  NaOH  +  H2 

The  hydroxide  dissolves  in  water  and  may  be  obtained  by 
evaporation.  A  large  amount  of  energy  is  liberated  in 
the  decomposition  of  water  by  sodium,  which  may  be 
readily  shown  by  dropping  a  piece  of  sodium  on  a  moist 
piece  of  filter  paper.  In  this  way  the  heat  is  all  liberated 
at  one  place  and  is  sufficient  to  ignite  the  hydrogen. 
On  account  of  its  ready  action  with  water,  the  sodium 
is  always  kept  under  kerosene  or  some  other  oil  containing 
no  oxygen,  or  in  air-tight  containers. 

135.  Uses  of  Sodium.  —  This  metal  is  used  for  making 
sodium    peroxide,   sodium   cyanide,   and    many   complex 
compounds  used  as  dyes  and  drugs.     Its  chemical  activity 
makes  it  valuable   for   the   laboratory   study   of  typical 
chemical  reactions. 

136.  Spectrum  Analysis.  — The  colors  imparted  to  flames 
by  different  elements  furnish  a  simple  and  valuable  method 
of  analysis.     The  different  colors  found  in  light  are  bent 
to  different  degrees  in  passing  through  a  prism,  and  are 
so  separated  from  each  other.     The  band  of  light  thus 
produced  is  known  as  a  spectrum,  and  the  instrument  used 
to  produce  and  view  the  spectrum  is  called  a  spectroscope. 
It  was  invented  by  Bunsen  and  Kirchhoff.    The.light  to  be 


138  SODIUM  AND  POTASSIUM 

studied  is  admitted  through  a  narrow  slit  ( A)  in  the  end 
of  a  tube,  in  such  a  way  that  it  will  fall  in  parallel  rays 
on  a  prism  ( <7)  with  its  edges  parallel  to  the  slit.  When 
the  beam  emerges  from  the  prism,  the  different  colors  are 
separated  and  the  spectrum  is  viewed  through  lenses  (J?) 
placed  at  the  end  of  another  tube  (Fig.  37). 

White  light,  produced  by  an  incandescent  solid,  gives  a 
spectrum  consisting  of  a  continuous  band  of  color,  shad- 
ing from  red  through  orange,  yellow,  green,  blue,  and 
indigo  to  violet.  When  the  light  is  due  to  incandescent 
vapors,  the  spectrum  consists  of  a  series  of  bright  lines, 
the  color  and  position  of  which  differ  for  each  element. 


FIG.  37.  —  DIAGRAMMATIC  REPRESENTATION  OF  SPECTROSCOPE. 

The  yellow  color  spoken  of  above  is  due  to  the  presence 
of  sodium  vapor  in  the  flame.  This  may  be  most  conven- 
iently produced  by  placing  in  a  flame  a  rod  of  common 
glass,  which  contains  a  sodium  compound.  Such  a  flame 
when  viewed  with  a  good  spectroscope  shows  two  yellow 
lines  very  close  together.  The  spectrum  of  potassium  con- 
sists of  a  double  line  in  the  violet  end  and  a  line  in  the 
red  end  of  the  spectrum. 

Lithium  is  a  rare  metal  closely  related  to  sodium  and 
potassium.  It  was  thought  to  exist  in  very  few  minerals 
until  the  spectroscope  showed  that  small  quantities  of  it 
were  widety  distributed  throughout  nature.  Its  spectrum 
consists  of  a  bright  red  line  and  a  very  faint  yellow  line. 


BASES  AND  NEUTRALIZATION  139 

The  presence  of  one  millionth  of  a  milligram  of  lithium 
can  be  shown  by  means  of  the  spectroscope. 

The  observance  of  unfamiliar  lines  in  the  spectra  of 
known  elements  has  led  in  several  instances  to  the  dis- 
covery of  elements.  By  its  spectrum,  helium  was  known 
to  exist  in  the  sun  before  this  element  was  found  in  the 
earth.  The  frontispiece  shows  the  spectrum  of  the  sun, 
and  that  of  a  number  of  elements.  The  last  two  ele- 
ments are  metals  of  the  rare  earths,  prsesodymium  and 
neodymium  respectively. 

137.  Bases.  —  A  solution  of  sodium  hydroxide  turns  red 
litmus  blue,  an  action  exactly  the  reverse  of  that  of  an 
acid.  Substances  behaving  like  sodium  hydroxide  in  this 
respect  are  said  to  have  an  alkaline  reaction. 

If  we  mix  solutions  containing  weights  of  hydrochloric 
acid  and  sodium  hydroxide  proportional  to  their  molecular 
weights,  there  is  a  rise  of  temperature,  and  the  resulting 
solution  affects  neither  red  nor  blue  litmus.  This  solution 
contains  sodium  chloride,  a  fact  that  is  clearly  indicated 
by  its  taste.  As  the  acid  and  the  hydroxide  have  both 
lost  their  characteristic  properties,  the  resulting  solution 
is  said  to  be  neutral  and  the  process  is  known  as  neutraliza- 
tion. The  change  may  be  expressed  by  the  equation  : 

HC1  +  NaOH— ^H20  +  NaCl 

Sodium  hydroxide,  because  of  its  action  with  acids,  is  a 
typical  base.  A_  base  is  the  hydrmridft  nf  a.  mp.t.a.1  or  of  a 
metallic  radical.  It  may  or  may  not  be  soluble  in  water. 
Copper  hydroxide  is  an  illustration  of  a  base  which  is  in- 
soluble in  water.  Water  solutions  of  bases  give  alkaline 
reactions.  Potassium  hydroxide  and  calcium  hydroxide 
are  two  other  common  soluble  bases. 


140 


SODIUM  AND  POTASSIUM 


138.  Preparation    of   Potassium.  —  Potassium    resembles 
sodium  in  so  many  respects  that  it  may  be  very  briefly 
discussed. 

Its  preparation  is  similar  to  that  of  sodium,  substituting 
potassium  hydroxide  for  sodium  hydroxide. 

139.  Properties   of  Potassium.  —  Potassium  is  a  silvery 
white  metal  with  a  slight  bluish  tinge.     It  is  softer  than 
sodium,  lighter,  and  melts  at  a  lower  temperature.     Al- 
though sodium  and  potassium  are  solids  at  ordinary  tem- 
peratures, an  alloy  of  the  two  can  be  prepared  that  is  a 
liquid. 

The  chemical  properties  of  potassium  closely  resemble 
those  of  sodium,  but  it  is  mofe  active.  It  decomposes 
water,  forming  potassium  hydroxide  and  liberating  hydro- 
gen. The  energy  produced  is  sufficient  to  ignite  the 
hydrogen,  as  the  potassium  skims  over  the  surface  (Fig. 
16,  page  35).  Potassium  imparts  a  reddish  violet  color  to 
the  flame.  As  the  presence  of  a  slight  trace  of  sodium 
obscures  the  potassium  flame,  several  thicknesses  of  cobalt 
blue  glass  should  be  interposed  between  the  flame  and  the 
eye  to  absorb  the  yellow  light  produced  by  sodium. 

SUMMARY 

Sodium  and  potassium  are  made  by  the  electrolysis  of  their 
hydroxides. 


ATOMIC  WT. 

SPECIFIC  GR- 

MELTING  PT. 

BOILING  PT. 

Sodium 

23.0 

.97 

97.6° 

877° 

Potassium 

39.1 

.87 

62.5° 

757° 

Both  metals  are  soft  and  light.     They  react  with  water  to  form 
hydroxides,  and  with  acids  to  form  salts. 


EXERCISES  141 

Their  compounds  are  characterized  by  the  colors  they  impart  to 
a  non-luminous  flame.  Most  of  the  compounds  are  colorless 
(white  when  powdered),  and  soluble  in  water,  the  potassium  com- 
pounds being  more  soluble. 

The  hydroxides  of  sodium  and  potassium  are  typical  bases  — 
caustic,  alkaline,  and  neutralizing  acids.     They  are  used  in  the 
preparation  of  soaps  and  bleaching  solutions,  in  oil-refining,  and 
.in  glass-making. 

EXERCISES 

1.  Why  was  the  preparation  of  metallic  sodium  a  difficult 
chemical  problem  to  solve  ?  ,  •  &U  CL£ 

2.  Does  melted  sodium  hydroxide  act  on  iron  and  nickel  ? 
Give  a  reason  for  your  answer.     't .  i  .  /bts&CUUAA~  sVb 

*3.  WEy  cannot  a  water  solution  of  sodium  hydroxide  be 
used  for  the  electrolytic  preparation  of  sodium  ?  ,. 

n  /*TT»  ^-f/j/     fyrvi'     ••faff'. '  -d'V'      f/    /i.\r^r!/.~^L'    AA/^-^'-'-t'    /yi,-'''£(*-  sTfyut^     ^T^**^'\/jw 

4.  Sketch  the  apparatus  for  making  sodium.     Label  each 
part.     What  are  the  uses  of  the  wire  gauze  ?     What  goes  to 
the  cathode  ?     To  the  anode  ? 

5.  Compare  the  properties  of  sodium  with  the  corresponding 
properties  of  metals  with  which  you  are  more  familiar,  for 
example,  iron,  copper,  silver.     Do  you  find  any  resemblances  ? 

6.  Why  is  sodium  classed  as  a  metal  ? 

'  ^f    s /^-f^L   t4n/*JLii.*s'rt'~i'  $j  •£*  id    %/  •£  ' 

7.  What  are  the  most  essential  properties  of  metals  from 

the  chemical  point  of  view  ? 

8.  Why  does  neither  sodium  nor  potassium  occur  in  an  un- 
combined  state  in  nature  ?    /£ 

9.  How  may  sodium  be  kept?     Explain. 

10.  What  properties  of  sodium  prevent  its  use  as  an  electric 
conductor  ? 

11.  Calculate  the  quantity  of  sodium  that  could  be  obtained 
from  1  kilogram  of  pure  sodium  hydroxide. 

12.  Why  would  it  be  extremely  dangerous  to  drop  into  water 
a  large  piece  of  sodium  or  potassium  ? 
^'^i!c^.^Ji^^,^f^i      $£  f-^       -  *  •   V 


/T7#*  ^  •   J 

142  SODIUM  AND  POTASSIUM 

13.  Write  the  equation  for  the  reaction  of  potassium  with 
water.     What  would  be  obtained  if  the  resulting  solution  were 
evaporated  to  dryness  ?   /t-?tt 

14.  Calculate  the  quantity  of  sodium  hydroxide  that  would 
be   formed   by   the  action  of   5  grams  of   sodium   on   water. 
What  weight  of  hydrogen  would  be  evolved  ?     What  volume 
would  the  hydrogen  have  under  standard  conditions  ? 

15.  'Is  potassium  hydroxide  a  base  ?     Why  ?  ^ 

,.  ,  '-*T/ 

16.  What  is  neutralization  ?J^ 

17.  What  weight  of  hydrogen  chloride  would  be  required  for 
the  complete  neutralization  of  2.63  grams  of  sodium  hydroxide? 

18.  What  right  have  we  to  believe  that  many  of  the  terres- 
trial elements  exist^  in  the  sun?  ^>j^,^f^hL^ti^ 

19.  Mention   two    methods   for    preparing   hydrogen   from    . 

water.    /&/ 

A      /  / 


CHAPTER   XVI 


SOLUTION1 

WE  have  found  that  many  of  the  reactions  studied  take 
place  only  in  the  presence  of  water,  even  though  the  water 
itself  does  not  react. 

140.  Conducting  Power  of  Solutions.  - 
We  have  already  seen  that  water  solu- 
tions of  sodium  chloride  and  sulphuric 
acid  (electrolysis  of  water)  readily  per- 
mit the  passage  of  the  current.  Solu- 
tions differ  from  each  other  greatly  in 
their  power  to  conduct  electricity.  We 
may  test  other  solutions  by  arranging 
a  circuit  that  includes  a  source  of  cur- 
rent, the  substance  to  be  tested,  and 
some  instrument  to  detect  the  passage  of 
the  current,  as  an  incandescent  lamp,  in 
series.  In  Fig.  38  is  a  beaker  (a)  contain- 
ing the  solution  to  be  tested,  and  6,  b 
are  electrodes  with  mercury  contacts. 

The  incandescent  lamp  serves  two 
purposes.  Its  resistance  cuts  down  the  current  to  a 
strength  suitable  for  passing  through  a  solution.  Secondly, 
if  the  lamp  lights,  the  current  must  be  passing  through 


FIG.  38.  —  DETERMI- 
NATION OF  ELEC- 
TROLYTES. 


TO  INSTRUCTOR.  —  Although  this  and  the  following  chapter 
may  be  taken  up  at  this  point,  many  instructors  prefer  to  postpone  their 
discussion  until  the  students  have  become  acquainted  with  a  wider  range 
of  chemical  phenomena. 

143 


144  SOLUTION 

the  liquid  in  the  circuit,  and  the  solution  is  a  conductor. 
The  brilliancy  with  which  the  lamp  glows  roughly  indi- 
cates how  well  the  solution  in  the  circuit  conducts. 

When  distilled  water  is  put  into  the  circuit,  the  lamp 
does  not  even  glow  ;  hence,  in  those  water  solutions  which 
are  conductors,  the  current  must  be  carried  by  the  aid  of 
the  dissolved  substance.  A  water- solution  of  hydrochloric 
acid  conducts  the  current  readily  ;  a  solution  of  sugar  fails 
to  conduct,  but  a  solution  of  sodium  hydroxide,  a  typical 
base,  proves  as  good  a  conductor  as  hydrochloric  acid. 
Solutions  of  sulphuric  acid,  potassium  hydroxide,  sodium 
chloride,  sodium  sulphate,  and  copper  sulphate  all  allow 
the  lamp  to  glow  brilliantly.  When  a  solution  of  acetic  acid 
is  tested,  the  lamp  barely  glows.  Glycerine,  alcohol,  and 
many  similar  compounds  are  found  to  be  non-conductors. 

'•  \    ' 

141.  Electrolytes  and  Non-electrolytes. —  Our  circuit  in- 
cludes two  different  classes  of  conductors.  The  first 
consists  of  solid  conductors,  chiefly  metallic,  such  as  the 
copper  wire  and  the  carbon  filament  of  the  lamp.  These 
conductors  undergo  no  permanent  change  in  carrying  the 
current.  The  other  class  includes  those  liquids  that  we 
have  found  to  be  conductors,  the  components  of  which  are 
free  to  move  toward  the  electrodes,  which  are  the  places 
where  the  current  enters  and  leaves  the  liquid.  In  these 
liquid  conductors,  the  transmission  of  electricity  is  attended 
by  the  decomposition  of  the  solute,  components  of 
which  may  be  liberated  at  the  electrodes.  A  liquid  that 
is  permanently  decomposed  during  the  passage  of  an  elec- 
tric current  is  called  an  electrolyte.  The  name  given  to  the 
process  is  electrolysis. 

Arranging  the  electrolytes  and  non-electrolytes  in  two 
columns,  we  obtain  results  similar  to  those  indicated  in 
the  table  : 


4UTt 


DEPRESSION  OF  THE  FREEZING,  POINT  ,  145 

/wflxtA*     *M,  -t-z-FiL,  JLA&^^w  4vjfasi*#( 

ELECTBOLTTBS  NOK-ELECTBOLTTES         / 

HJ,     hydrochloric  acid     Ci  *&&-        distilled  water  f^ 

sulphuric  acid  fa/Vu&> 

faji,  sodium  hydroxide  ,  ^     ~~  sugar 
JrtM,  potassium  hydroxide  A4~* 

/:/  sodium  chloride       bfrcL       glycerine    . 
sodium  sulphate 

<2^^  copper  sulphate  alcohol 

'/v^,  <sf**J^    A.j^A.    '*/    ^j>*^ 


An  examination  of  the  column  of  electrolytes  shows  that 
it  contains  only  acids,  bases,  and  salts.  All  electrolytes 
belong  to  these  classes  of  compounds.  The  non-elec- 
trolytes in  the  second  column  are  not  generally  placed 
in  any  of  these  classes  of  compounds.  Why  is  it  that 
water  solutions  of  acids,  bases,  and  salts  conduct  elec- 
tricity, while  other  substances  fail?  This  question  has 
led  to  a  more  careful  study  of  the  properties  of  water 
solutions. 

142.  Effect  of  Dissolved  Solids  on  the  Freezing  Point.— 
Under  ordinary  conditions  of  pressure  pure  water  freezes 
at  0°  C.  and  boils  at  100°  C.  The  addition  of  any  soluble 
solid  lowers  the  freezing  point  and  raises  the  boiling 
point.  We  shall  discuss  only  the  freezing  point.  All 
water  solutions  freeze  at  a  lower  temperature  than  pure 
water.  Careful  measurements  show  that  the  amount  of 
the  lowering  depends  on  the  mass  of  the  substance  added. 
A  solution  containing  10  grams  of  sugar  to  one  liter  of 
water  will  freeze  at  a  point  twice  as  far  below  0°  as  one 
containing  5  grams  of  sugar  to  1  liter  of  water.  Accord- 
ing to  the  atomic  theory  10  grams  of  sugar  contain  twice 
as  many  molecules  as  5  grams.  .  Therefore,  the  lowering 
of  the  freezing  poiat  of  the  pure  solvent  is  proportional  to 
the  number  of  sugar  molecules  dissolved. 


146 


SOLUTION 


The  depression  of  the  freezing  point  of  water  (Fig.  39)1 
produced  by  equal  numbers  of  molecules  of  different  sub- 
stances has  been  carefully  determined.  To 
get  equal  numbers  of  molecules,  a  weight  in 
grams  equal  to  the  molecular  weight  of  each 
substance  was  dissolved  in  1  liter  of  water. 
Thus  46  grams  of  alcohol,  C2H5OH,  and 
342  grams  of  sugar,  C^H^O^  were  each 
dissolved  in  a  liter  of  water.  In  both  cases 
the  resulting  solutions  froze  at  —  1.86°.  It 
was  further  found  that  a  solution  of  any 
non-electrolyte  containing  a  gram-mo- 
lecular weight  of  the  solute  to  the  liter 
gave  this  same  lowering  of  the  freezing 
point.  If  weights  of  non-electrolytes  pro- 
portional to  their  molecular  weights  are 
dissolved  in  equal  volumes  of  the  same 
solvent,  the  solutions  will  freeze  at  the  same 
temperature.  This  is  strictly  true  for  dilute 
solutions  only.  This  indicates  that  the  de- 
pression of  the  freezing  point  is  dependent 
on  the  number  of  molecules  present  and  not 
on  the  weight  or  kind  of  these  molecules. 
But  if  common  salt  is  used,  we  find  that, 
in  dilute  solution,  the  freezing  point  is 
lowered  nearly  twice  as  much  as  in  the  case 
of  a  solution  of  a  non-electrolyte  containing  the  same 
number  of  molecules.  This  can  be  explained  by  as- 

1  Figure  39  represents  an  apparatus  for  determining  the  depression  of 
the  freezing  point.  A  Beckmann  thermometer  (a)  is  used  and  the  liquid 
to  be  frozen  is  held  in  the  inner  tube  (6).  Through  the  side  tube  (c)  is 
introduced  the  substance  whose  effect  on  the  freezing  point  of  the  pure 
solvent  is  to  be  determined.  A  stirring  rod  (c?)  moves  up  and  down  in 
the  solution,  which  is  cooled  by  a  freezing  mixture  contained  in  the  outer 


FIG.  39. 


MEASUREMENT  OF  OSMOTIC  PRESSURES     147 

sumiiig  the  presence  of  twice  as  many  particles  in  a 
solution  containing  a  molecular  weight  of  salt  as  in  the 
same  volume  of  a  solution  containing  a  molecular  weight 
of  sugar.  In  other  words,  we  have  reason  to  think  that 
when  they  are  dissolved  in  water,  all  or  nearly  all  of  the 
salt  molecules  are  separated,  each  into  two  particles. 
Other  electrolytes  behave  as  salt  does,  while  non-electro- 
lytes act  like  sugar. 

143.  Osmotic  Pressure.  —  The  effect  of  solutes  in  raising 
the  boiling  points  and  lowering  the  freezing  points  of  sol- 
vents  is  closely  connected  with  what   is   called  osmotic 
pressure.     A    crystal   of   copper  sulphate   placed  at  the 
bottom  of  a  tall  cylinder  of  water  will  finally  distribute 
itself  uniformly  throughout  the  liquid.     A  considerable 
weight  of  the  copper  sulphate  thus  rises  in  spite  of  the 
attraction  of  gravitation,  indicating  that  a  pressure  is  at 
work. 

It  is  believed  that  the  particles  of  copper  sulphate 
move  at  high  velocities  as  they  leave  the  crystal.  They 
travel  in  straight  lines  until  they  strike  other  particles  or 
one  of  the  surfaces  that  inclose  the  liquid,  when  they  re- 
bound, still  moving  at  high  velocities.  In  other  words, 
the  dissolved  particles  are  believed  to  act  like  the  mole- 
cules of  a  gas,  and  a  pressure  is  produced,  just  as  it  is  in 
a  gas,  by  the  impacts  of  the  moving  particles.  This  is 
known  as  osmotic  pressure. 

144.  Measurement  of  Osmotic  Pressures.  —  This  is  accom- 
plished by  the  use  of  cells  that  contain  within  their  walls 
membranes  through  which  water,  but  not  the  solute,  can 
pass  (Fig.  40).     These 'are  called  semi-permeable  mem- 
branes.    The   osmotic   pressure   in  even  a  fairly   dilute 
solution  is  enormous.     The   solution   therefore   tends  to 


148 


SOLUTION 


expand,  .and  so  to  become  more  dilute.  This  possibility 
exists  if  the  solution  is  contained  in  a  semi-permeable  cell 
which  is  surrounded  by  water.  The  water  will  enter, 
diluting  the  solution  until  a  water 
pressure  is  produced  that  equals 
the  osmotic  pressure. 


145.  Analogy  between  Osmotic 
Pressure  and  Gas  Pressure.  —  Osmotic 
pressures,  like  gas  pressures,  are 
found  to  depend  on  the  number 
and  not  on  the  kind  of  particles  that 
cause  them.  Boyle's  and  Charles' 
Laws  apply  also  to  osmotic  pres- 
sures. A  statement  analogous  to 
Avogadro's  Hypothesis  can  be  made 
concerning  the  number  of  dissolved 
particles  in  equal  volumes  of  solu- 
tions at  equal  temperatures  and 
equal  osmotic  pressures.  In  fact, 
the  solute,  in  producing  this  pres- 
sure, acts  as  if  it  were  a  gas  con- 
fined within  a  volume  equal  to  that 
of  the  solvent. 


FIG.  40.  —  OSMOTIC  CELL. 
A,    semi-permeable    cell; 

B,  glass  connecting  tube; 

C,  mercury    gauge    to 
show  pressure  produced. 


146.  Dissociation  of  Electrolytes.  —  A  careful  study  of  the 
boiling  point  shows  a  greater  elevation  in  the  case  of 
electrolytes  than  in  non-electrolytes,  in  proportion  to  the 
number  of  dissolved  molecules.  The  differences  in  the 
freezing  point  and  boiling  point,  produced  by  equal  num- 
bers of  molecules  of  electrolytes  and  non-electrolytes, 
may  all  be  explained  by  assuming  that  in  electrolytes 
the  dissolved  molecules  are  broken  up  or  dissociated  into 
parts  as  soon  as  they  are  dissolved.  In  non-electro- 


Michael  Faraday  (1791-1867),  the  son  of  a  blacksmith,  was 
born  in  a  suburb  of  London.  At  the  age  of  fourteen  he  was  ap- 
prenticed to  a  bookbinder,  but  devoted  his  spare  time  to  reading 
and  attending  lectures  on  physical  science.  He  heard  Davy  lecture 
at  the  Royal  Institution  and  wrote  him,  expressing  a  desire  to  enter 
the  service  of  science.  He  became  Davy's  laboratory  assistant  in 
1813.  Faraday  sacrificed  much  in  order  to  devote  his  time  to  pure 
science,  and  his  discoveries  are  numerous,  including  benzene, 
magneto-electric  induction,  electrochemical  equivalents,  and  the 
liquefaction  of  several  gases.  He  expressed  the  belief  that  gases 
are  liquids  having  a  very  low  boiling  point. 


IONS  149 

lytes  the  molecules  of   the  dissolved  substance  are  not 
dissociated.  S 

JF 

147.  Chemical  Activity  of  Electrolytes.  —  We  have  already 
noted  the  fact  that  acids,  bases,  and  salts  are  electrolytes; 
these  are  the  substances  that  we  have  made  use  of  in  the 
greater  part  of  our  chemical  actions  so  far.     Nearly  all 
chemical  actions  require  the  presence  of   water.     When 
two  solutions  .of  electrolytes  are  mixed,  action  takes  place 
rapidly  if  one  of  the  products  of  the  reaction  is  either  in- 
soluble or  gaseous.     So  we  may  say  that  in  general  elec- 
trolytes  are   very,  active  chemically.      Non-electrolytes, 
on  the  other  hand,  usually  show  very  little  activity. 

148.  Ions.  —  To  the  moving  particles  that  are  formed 
in  the  electrolyte  while  solution  is  taking  place  Faraday 
gave  the  name  ions,  meaning  wanderers.     We  have  just 
seen  that  the  hydrochloric  acid  molecule  is  broken  up, 
in  the  act  of  dissolving,  into  two  particles ;  these  must  be 
the  hydrogen  and  chlorine  atoms.     Why  do  they  move 
in  opposite  directions  ?     Bodies  with  electrical  charges  of 
opposite  kind  attract   each   other.     Since   the   hydrogen 
particles  in  a  water  solution  are  attracted  toward  the  cath- 
ode, or  negative  pole,  these  hydrogen  particles  must  be 
positively  charged.     Similarly  the  chlorine  particles  must 
have  negative  charges,  since  they  are  drawn  toward  the 
positive  pole  or  anode. 

When  a  solution  of  copper  sulphate  is  electrolyzed,  cop- 
per appears  at  the  cathode  and  experimental  evidence 
shows  the  presence  of  combined  sulphur  and  oxygen  at 
the  anode.  The  copper  sulphate  must  therefore  dissociate 
while  dissolving  into  Cu,  a  positive  (  +  )  ion,  and  SO4,  a 
negative  (  — )  ion.  An  ion,  then,  is  an  atom  or  group  of 
atoms  carrying  an  electric  charge. 


150  SOLUTION 

149.  Osmotic  Pressures  as  a  Proof  of  lonization.  —  In  solu- 
tions of  electrolytes  we  find  abnormally  high  osmotic  pres- 
sures.   If  the  substance  is  one  that,  like  hydrogen  chloride, 
gives  only  two  ions,  the  pressure  will  be  twice  that  of  a 
similar  solution  of  a  non-electrolyte.     This  is   what   we 
would  expect  from  the  theory  of  ionization,  and  the  agree- 
ment constitutes  a  striking  proof  of  the  theory. 

\  -;(L»    Ct 
i/iM     Y^  _^ 

150.  Explanation  of  Electrolysis.  —  Sodium  chloride  disso- 
ciates in  water  into  sodium  and  chlorine  ions.     From  the 
intensity  with  which  sodium  ordinarily  reacts  with  water, 
we  might  expect  the  instant  formation  pf  sodium  hydrox- 
ide.    But  this  cannot  be  present,  for  the  solution  is  per- 
fectly neutral  in  reaction.     The  sodium  ion  does  not  react 
with  water.     But  when  a  current  is  passed  through  a  solu- 
tion, the  positive  charges  of  the  sodium  ions  are  neutralized 
by  contact  with  the  negative  electrification  of  the  cathode ; 
the  sodium  ions  then  become  sodium  atoms  and  react  with 
the  water  surrounding  the  cathode,  forming  sodium  hy- 
droxide.    It  should  be  understood,  however,  that  the  elec- 
tric current  is  not  the  cause  of  the  dissociation  into  charged 
particles,  but  simply  determines  the  direction  in  which  they 
move.      The  dissociation  took  place  while  the  substance 
was  dissolving. 

The  chlorine  ions  give  up  their  negative  charges  the 
instant  they  touch  the  anode,  neutralizing  in  part  the 
positive  charge  on  that  electrode.  The  particles  of  chlo- 
rine without  their  charges  are  ordinary  atoms,  which  unite 
in  pairs  to  form  molecules  of  chlorine  gas,  which  bubbles 
off  at  the  anode. 

151.  Differences  between  Ion  and  Atom.  —  Ions   should 
not  be  confused  with  atoms.     The  existence  of  an  electric 
charge  on  an  atom  entirely  changes  its  properties,  as  may 


IONIZAT10N  OF  ACIDS  AND  BASES  151 

be  seen  from  the  electrolysis  of  sodium  chloride  just  de- 
scribed. Atoms  of  chlorine  tend  to  combine  in  pairs  to 
form  molecules  of  green  chlorine  gas ;  ions  of  chlorine  are 
colorless  and  repel  each  other  because  they  possess  like 
charges. 

The   differences   between   ion   and   atom  may  now  be 
stated,  as  follows  :  first,  an  ion  has  an  electric  charge,  an 
atom  has  not ;  second,-  a  single  ion  often  includes  several 
atoms  of  different  elements. 
I   ;4^''    -£f--*T^        *J?£~-  (L-h/£t>1  j  *-" 

152.  lonization  of  Acids  and  Bases.  —  When  an  electrolyte 
is  dissolved  in  water,  some  of  its  molecules  enter  the  solu- 
tion undissociated,  while  the  other  molecules  separate  into 
particles  which  become  electrically  charged  in  the  process. 
On  passing  the  current  through  a  solution  of  hydrochloric 
acid,  we  find  hydrogen  collecting  at  the  cathode  and  chlo- 
rine at  the  anode.  In  the  solution  there  must  be  positively 
charged  hydrogen  ions  and  negatively  charged  chlorine 
ions.  The  electrolysis  of  nitric  acid  reveals  the  presence 
\  of  hydrogen  ions  and  NO3  ions ;  that  of  sulphuric  acid 
"'  shows  two  hydrogen  ions  and  one  SO4  ion  for  each  molecule 
'  dissociated.  The  electrolysis  of  other  acids  gives,  in  every 
case,  hydrogen  at  the  cathode  and  so  indicates  the  presence 
of  hydrogen  ions.  To  these  are  ascribed  the  characteristic 
properties  of  acids.  This  hydrogen  ion,  common  to  all  acids, 
is  responsible  for  the  sour  taste,  and  for  turning  litmus 
red.  The  presence  of  hydrogen  in  a  compound  does  not 
make  it  an  acid ;  the  compound  must  give  hydrogen  ions 
in  water  solution.  Liquefied  hydrogen  chloride,  free  from 
water,  fails  to  act  as  an  acid,  because  none  of  its  molecules 
break  up  so  as  to  give  hydrogen  ions.  An  acid  is  a  hy- 
drogen compound  whose  water  solution  contains  hydrogen  ions. 
When  bases  are  dissolved  in  water,  the  metallic  atom 
in  the  molecule  becomes  the  positive  ion  and  the  hydroxyl 

VLW        /A' 


152  SOLUTION 

group  the  negative  ion.  The  hydroxyl  ions  are  the  only 
ions  common  to  all  bases,  and  to  them  the  characteristic 
properties  of  bases  are  attributed.  Hence  the  definition  : 
'  A  base  is  a  hydroxide  whose  water  solution  contains  hydroxyl 
ions. 

•JJ 

\  v  153.  Effect  of  Dilution  on  lonization.  — It  will  be  readily 
seen  that  the  more  ions  there  are  present  in  a  given  solu- 
tion, the  better  it  will  conduct  the  current,  for  the  ions 
act  as  carriers.  So  we  can  measure  the  degree  of  ioniza- 
tion  by  the  conducting  power  of  the  solution,  provided 
there  is  the  same  weight  of  solute  between  the  electrodes 
in  every  case.  Conductivity  under  these  conditions  is 
called  molecular  conductivity.  We  find,  as  we  continue 
to  dilute  an  electrolyte,  that  the  molecular  conductivity  in- 
creases up  to  a  certain  point,  beyond  which  it  does  not 
change.  This  might  be  expected,  for  at  a  certain  dilution 
all  the  molecules  are  dissociated,  and  a  furthur  dilution 
causes  no  further  dissociation.  The  effect  of  dilution  on 
ionization  is  shown  in  the  following  table,  in  which  m  is 
the  number  of  gram  molecules  in  1000  grams  of  water. 
The  numbers  give  the  relative  conductivity. 

HNOs  HCl  KC1  NaCl 


1.00 

2770 

2780 

919 

695 

0.50 

2991 

3017 

958 

757 

0.10 

3225 

3244 

1047 

865 

0.05 

3289 

3330 

1083 

897 

0.01 

3395 

3416 

1147 

962 

154.  Activity  of  Acids  and  Bases.  —  The  chemical  activity 
of  an  acid  depends  upon  the  extent  to  which  its  dissolved 
molecules  are  dissociated  into  ions.  Hydrochloric  acid  is 
almost  wholly  dissociated  into  its  ions  in  dilute  solution. 


Svante  August  Arrhenius 
was  born  at  Wijk,  Sweden, 
in  1859.  He  is  the  present 
director  of  the  Physico-chem- 
ical Department  of  the  Nobel 
Institute.  His  great  work  was 
the  invention  in  1887  of  the 
modern  theory  of  dissociation 
in  electrolytes,  commonly 
known  as  the  ionization  hy- 
pothesis. This  conception  has 
done  much  to  bind  into  an 
orderly  system  many  previ- 
ously unexplained  experi- 
'  observations.  '.  • , \' 


Jacobus  Henricus  van't 
Hoff  (1852-1911)  was  born 
at  Rotterdam,  Holland.  He 
become  Professor  of  Physical 
Chemistry  to  the  University  of 
Berlin  in  1894.  He  possessed 
great  depth  of  scientific  imagi- 
nation and  will  be  remembered 
for  his  brilliant  work  in  devel- 
oping several  of  the  general- 
izations of  modern  physical 
chemistry  and  for  the  appli- 
cation of  physical  chemistry 
to  geology. 


\ 


EXPLANATION  OF  NEUTRALIZATION          153 

This  is  why  it  acts  vigorously  on  metals  and  neutralizes 
bases.  Such  an  acid  is  spoken  of  as  a  strong  acid.  Nitric 
acid  is  another  example  of  a  strong  acid.  Sulphuric  acid,  I 
which  is  dissociated  but  two  thirds  as  much  as  the  acids 
just  mentioned,  is  not  so  strong  an  acid.  Acetic  acid  is 
the  type  of  a  weak  acid,  because  it  is  so  slightly  dissociated 
(less  than  2%  in  dilute  solution)  that  it  does  not  act 
vigorously  on  most  metals,  and  its  reactions  with  other 
substances  are  slow. 

The  term  strength  of  acid  must  not  be  confused  with 
the  term  concentrated  acid.  Concentrated  sulphuric  acid 
usually  contains  about  95%  H2SO4,  while  concentrated 
hydrochloric  contains  but.  37%  HC1.  Sulphuric  acid, 
then,  is  usually  the  more  concentrated,  but  it  is  the 
weaker  acid  of  the  two.  Hydrochloric  acid  is  the 
more  reactive,  since  it  is  dissociated  to  a  greater  extent 
in  water  solution.  In  the  preparation  of  hydrogen  chlo- 
ride, the  reason  for  the  displacement  of  hydrochloric  acid 
by  sulphuric  acid  is  not  that  sulphuric  acid  is  a  stronger 
acid,  but  that  it  has  a  higher  boiling  point. 

As  in  the  case  of  acids,  the  strength  of  a  base  depends 
upon  the  degree  of  ionization  it  undergoes  in  solution. 
Sodium  hydroxide  and  potassium  hydroxide  are  almost 
completely  dissociated  in  dilute  solutions.  They  are  types 
of  strong  bases. 


155.  Explanation  of  Neutralization.  —  When  we  mix  dilute 
solutions  of  hydrochloric  acid  and  sodium  hydroxide,  we 
have  present  in  the  mixture  positive  ions,  hydrogen  and 
sodium,  and  negative  ions,  chlorine  and  hydroxyl.  Each 
positive  hydrogen  ion  will  attract  a  negative  hydroxyl  ion, 
and  vice  versa.  The  two  ions  combine,  the  equal  opposite 
charges  neutralize  each  other,  and  a  molecule  of  undis- 
sociated  water  results.  Indicating  the  sign  of  the  charge 


154  SOLUTION 

by  a  +  or  —  above  and  to  the  right  of  the  symbol,  we  may 
express  this  charge  by  the  equation : 

H++OH-  — ^H20 

As  the  water  formed  is  practically  un)dissociated  (only  two 
molecules  in  a  billion),  we  may  consider  it  as  completely 
removed  from  the  action  as  if  it  had  formed  an  insoluble 
compound  or  precipitate.  In  the  neutralization,  for  each 
H+  ion  withdrawn  in  this  way  a  Cl~  ion  is  left,  and  for 
each  OH~ion  a  Na+ ion  remains.  These  will  not  unite 
permanently  so  long  as  water  is  present,  for  the  sodium 
chloride  is  dissociated  as  fast  as  it  is  formed.  The 
neutralization  is  complete,  when  there  are  neither  H+ 
nor  OH~  ions  left  to  give  an  acid  or  a  basic  reaction,  and 
the  solution  then  contains  equal  numbers  of  Na+  and  Cl~ 
ions.  The  equation  showing  these  facts  is : 

H+  +  Cl-  +  Na+  +  OH-  — ^  H2O  +  Na+  +  Cl~ 

If  the  solution  is  now  concentrated,  the  degree  of  dissocia- 
tion is  lessened,  and  Na+  and  Cl~  ions  will  unite  to  form 
undissociated  sodium  chloride.  When  evaporation  is  com- 
plete, we  find  that  they  have  completely  united,  forming 
crystals  of  salt. 

r 

156.  Products  of  Neutralization.  —  We  get  similar  results 
from  the  use  of  other  acids  and  bases.  Potassium  hydrox- 
ide and  hydrochloric  acid  give  water,  K+  ions  and  01"  ions. 
Nitric  acid  and  sodium  hydroxide  yield  undissociated 
water,  Na+  ions  and  NOg  ions. 

K++OH-+H++C1-    — ->-H2O  +  K+   +  01- 
Na++  OH-+  H++  NOg  — >-  H2O  +  Na++  NOg 

In  every  case  of  neutralization  the  products  are: 


CHARGES   CARRIED  BY  IONS  155 

(1)  undissociated  water; 

(2)  a  solution  containing  positive  ions  from  the  base 

and  negative  ions  from  the  acid ; 

(3)  energy  in  the  form  of  heat. 

During  the  evaporation  of  the  solvent  the  positive  ions 
from  the  base  unite  with  the  negative  ions  from  the  acid 
to  form  a  compound  known  as  a  salt. 

157.  Heat  of  Neutralization. — Neutralization,  as  a  chemical 
process,  is  essentially  the  formation  of  undissociated  water 
molecules.  It  is  always  accompanied  by  the  liberation  of 
heat.  When  dilute  solutions,  containing  equal  amounts  of 
a  strong  acid,  are  neutralized  by  different  strong  bases,  the 
same  quantity  of  heat  is  produced  in  each  case.  This  heat 
is  known  as  the  heat  of  neutralization. 

Table  showing  heat  of  neutralization  expressed  in  calo- 
ries, using  gram-molecular  weights : 

HC1  HN03 


NaOH        13,700  cal.  13,700  cal. 

KOH        13,700  cal.  13,700  cal. 

This  uniformity  in  the  heat  of  neutralization  indicates  that 
the  action  is  the  same  in  all  these  cases.  The  only  com- 
mon product  is  water.  Therefore,  the  heat  of  neutraliza- 
tion is  the  heat  evolved  by  the  formation  of  water  from  hydro- 
yen  and  hydroxyl  ions. 

158.  Charges  carried  by  Ions.  —  We  have  seen  that  one 
molecule  of  hydrochloric  acid  neutralizes  one  molecule  of 
sodium  hydroxide,  producing  one  molecule  of  water.  But 
we  find  that  to  neutralize  one  molecule  of  barium  hydrox- 
ide, Ba(OH)2,  two  molecules  of  hydrochloric  acid  are  re- 
quired, according  to  the  equation: 

Ba(OH)2  +  2  HCl-^-2  H2O  +  BaCl2 


156 


SOLUTION 


The  barium  chloride  is  largely  dissociated  into  barium  and 
chlorine  ions.  In  any  solution,  the  positive  charges  must 
equal  the  negative  charges.  Therefore,  in  this  case  each 
barium  ion  must  contain  two  positive  charges  to  equal  the 
negative  charges  on  the  two  chlorine  ions.  Sulphuric  acid 
dissociates  into  H+,  H+,  and  SO4  ions;  the  SO4  —  ion 
must  carry  two  negative  charges  to  balance  the  positive 
charges  of  the  two  hydrogen  ions. 


Some  other  ions  carry  three  and  even  four  charges. 


No.  OF 
CHARGES 

POSITIVE  IONS 

NEGATIVE  IONS 

1 

H,  Na,  K,  Li,  Ag,  NH4, 

OH,  F,  Cl,  Br,  I,  N03, 

C1O3,  and  other  nega- 
tive ions  of  mono- 
basic acids  • 

^2 

Ca,  Sr,  Ba,  Mg,  Zn,  Hg,  Co,  Ni, 
Cu  (cupric),  Fe  (ferrous), 
Sn  (stannous) 

S,  SO4,  CO3,  and  other 
negative   ions  of   di- 
f  basic  acids 

3 

Al,  Bi,  Sb,  Fe  (ferric) 

PO4  and  other  negative 
ions  of  tribasic  acids 

4 

Sn  (stannic) 

SiO4  and  negative  ions 
of  tetrabasic  acids 

The  preceding  table  shows  the  common  ions  with  the 
number  of  charges  carried  by  each  and  the  signs  of  the 
charges. 

159.  Valence  of  Ions.  —  Atoms  differ  with  respect  to  the 
number  of  atoms  of  other  elements  with  which  they  com- 
bine. We  have  defined  this  as  valence  (§  111). 

In  electrolytes,  the  valence  of  each  ion  is  numerically 
equal  to  the  number  of  charges  carried  by  it.  This,  of 


SUMMARY  157 

course,  does  not  explain  the  valence  of  atoms  in  non- 
electrolytes,  but  does  indicate  a  connection  between  the 
valence  and  the  electrical  capacity  of  an  atom  in  an 
electrolyte. 

160.  lonization  in  Other  than  Water  Solution.  —  While 
ionization  takes  place  to  a  higher  degree  in  water  than  in 
other  solvents,  it  seems  certain  that  the  separation  takes 
place  to  at  least  a  small  extent  in  every  case  of  solution. 
The  power  of  a  solvent  to  cause  ionization  depends  on 
several  of  its  properties,  an  important  one  being  the  degree 
to  which  the  substance  limits  the  force  of  attraction  be- 
tween positively  and  negatively  charged  bodies.  Water 
does  this  to  a  considerable  degree,  hence  there  is  much 
tendency  for  ions  to  remain  apart  in  water  solution.  Methyl 
alcohol  offers  less  hindrance  to  the  attraction,  and  we  find, 
as  the  theory  indicates,  that  methyl  alcohol  is  only  a  fairly 
good  ionizing  solvent.  Benzene  offers  very  little  hin- 
drance, and,  as  we  would  expect,  there  is  almost  no  ioniza- 
tion in  this  medium. 

Fused  salts,  even  in  the  complete  absence  of  water, 
often  conduct  an  electric  current.  This  indicates  ion- 
ization. 

With  the  careful  study  that  has  followed  the  develop- 
ment of  the  hypothesis  of  ionization,  chemists  have  come 
to  believe  that  in  the  great  majority  of  cases  chemical 
action  occurs  between  ions  and  not  between  molecules. 
With  the  aid  of  this  theory  many  things  not  previously, 
understood  have  been  fully  explained. 

SUMMARY 

Solutions  are  classified  as  electrolytes  and  non-electrolytes,  ac- 
cording to  their  conducting  power.  The  electrolytes  include  solu- 
tions of  acids,  bases,  and  salts. 


158  SOLUTION 

The  effect  of  dissolved  substances  on  the  boiling  point,  freezing 
point,  and  osmotic  pressure  indicates  that  the  molecules  of  the  solute 
are  dissociated  in  the  case  of  electrolytes.  Electrolytes  are  more 
active  chemically  than  non-electrolytes. 

The  portions  into  which  a  molecule  dissociates  are  ions  and 
carry  equal  and  opposite  electric  charges.  When  an  electric  cur- 
rent is  passed  through  an  electrolyte,  each  ion  passes  to  the  elec- 
trode of  opposite  sign  and  is  there  discharged  and  liberated.  Acids 
furnish  hydrogen  ions  in  solution;  bases  furnish  hydroxyl  ions, 
and  salts  furnish  other  ions.  The  percentage  of  ionization  increases 
with  the  dilution  until  ionization  is  complete. 

The  strong  or  active  acids  and  bases  are  those  which  are  highly 
dissociated.  The  essential  action  in  neutralization  is  the  union  of 
the  hydrogen  and  hydroxyl  ions  to  form  undissociated  water ;  dur- 
ing the  evaporation,  the  union  of  the  other  ions  to  form  a  salt  is 
completed.  The  strong  acids  and  bases  unite  with  the  same  heat 
of  neutralization  for  equivalent  quantities. 

Hydrogen  and  metallic  ions  carry  positive  charges ;  the  non- 
metallic  ions,  negative  charges.  The  valence  of  an  ion  is  numeri- 
cally equal  to  the  number  of  charges  carried  by  it. 


EXERCISES 

1.  State  and  explain  on  the  basis  of  the  theory  of  elec- 
trolytic dissociation,  what  happens  when  a  current  of  electricity 
is  passed  through  a  solution  of  sodium  chloride. 

2.  How  do  you  determine  whether  a  given  solution  is  an 
electrolyte  ? 

3.  When  a  beaker  of  acetic  acid  is  put  in  circuit  with  an 
incandescent  lamp,  the  lamp  glows  feebly,  while  the  solution 
of  sodium  acetate  allows  it  to  glow  brightly.     What  does  this 
show? 

4.  Compare  the  freezing  point  of  sea  water  with  that  of 
ordinary  rain  water. 


EXERCISES  159 

5.  Why  will   substances   often  react  with  each  other  in 
solution  while  they  will  not  in  a  dry  state  ? 

6.  What  ions  are  present  in  solutions  of  the  following: 
KC1,  ZnSb«  KC103,  NaOH  ? 


7.  Distinguish  carefully  between  an  ion  of  potassium  and 
an  atom  of  potassium. 

8.  What  element  is  common  to  all  acids  ?  ^-What  group  of 
elements  is  common  to  all  bases  ?0j&elect  an  acid  and  a  base 
and  by  an  equation  show  that  you  understand  the  meaning  of 
the  term  neutralization. 

9.  Show  two  essential  differences  between  a  solution  of  salt 
in  water  and  the  suspension  of  an  insoluble  powder  in  water. 

10.  Why  is  nitric  acid  a^  more  active  acid  than  sulphuric 
acid  ?    $4  ^4 

11.  Give  the   changes   that  take   place  and  the  products 
formed  in  the  following  cases  : 

(a)  when  nitric  acid  is  added  to  water  ; 

(6)  when  a  piece  of  caustic  potash  is  dissolved  in  water  ; 

(c)  when  the  two  solutions  are  mixed. 

12.  A  piece  of  red  litmus  turns  blue  in  a  solution  of  sodium 
carbonate  (Na^COg).     Name  the  ions  shown  to  be  present  by 
this  test 

13.  Write  equations,  indicating  ions,  for  the  neutralization 
of  potassium  hydroxide  with  sulphuric  acid;    of   nitric  acid 
with  ammonium  hydroxide* 


-  V         ft  \    It/,     T          *>      ^ 

'  /      Co    J  ^y  /     2  /7 

V  » 


y        - 

i^A-f  ^#-/,?fy-      .^ 

J    -/  foi+fyj  W.  -+#  Orh-j  %* 

^T  1*.  ^J 


CHAPTER   XVII 

CHEMICAL  EQUILIBRIUM 

161.  Reversible  Reactions.  —  We  have  already  had  occa- 
sion to  point  out  that  some  chemical  actions  "  work  back- 
wards." For  example,  we  may  write  the  equation  : 

3  Fe  +  4  H20  ^±1  Fe8O4  +  8  H 

This  reaction  goes  one  way  or  the  other  according  to  the 
conditions  that  we  establish.  If  we  keep  a  current  of 
steam  passing  over  hot  iron,  it  proceeds  from  left  to  right  ; 
if  we  pass  hydrogen  over  hot  iron  oxide,  it  goes  from  right 
to  left. 

lonizations  are  also  excellent  examples  of  reversible 
action  : 


If  we  dissolve  salt  in  water,  the  action  goes  to  the  right  ; 
if  we  evaporate  water  from  the  solution,  the  action  goes 
to  the  left. 

162.  Dynamic  Equilibrium.  —  In  a  solution  of  sodium 
chloride;  provided  it  is  not  extremely  dilute,  we  always 
find  molecules  as  well  as  the  two  kinds  of  ions.  The 
ratio  between  the  dissociated  and  the  undissociated  mole- 
cules does  not  change  so  long  as  the  volume  of  the  solu- 
tion and  its  temperature  remain  constant.  In  other 
words,  a  condition  of  equilibrium  exists.  But  there  are 
many  reasons  for  believing  that  this  is  not  a  -motionless 

160 


DYNAMIC  EQUILIBRIUM  161 

equilibrium.  On  the  contrary,  it  is  supposed  that  both 
the  reactions  indicated  in  the  above  equation  are  con- 
stantly taking  place,  and  that  the  condition  of  equilibrium 
results  because  the  action  is  proceeding  just  as  fast  one 
way  as  the  other.  Thus  we  have  a  balanced  condition. 
This  is  described  as  dynamic  (i.e.  moving)  equilibrium. 

Consider  again  the  action  between  copper  and  water. 
The  two  constituents  are  heated  in  a  sealed  glass  tube. 
Under  this  condition  no  substance  can  escape.  Conse- 
quently, after  a  little  hydrogen  and  copper  oxide  have 
been  formed,  they  immediately  begin  to  act  on  each  other, 
independently  of  the  action  which  produced  them,  pro- 
ducing copper  and  water  again.  In  the  beginning  the 
direct  action  proceeds  with  the  greater  speed;  but  the 
reverse  action  gradually  gains,  until  finally  they  are  going 
with  equal  speeds,  thus  balancing  each  other,  so  that  the 
action  seems  to  stop.  Now  if  we  seal  equivalent  quantities 
of  copper  oxide  and  hydrogen  in  a  second  tube  and  heat 
them,  we  arrive  at  exactly  the  same  result  as  in  the  first 
tube ;  that  is,  we  have  all  four  substances,  copper,  copper 
oxide,  water,  and  hydrogen,  and  we  have  them  in  the 
same  proportion  as  in  the  first  tube.  This  fact  tends  to 
confirm  our  belief  that  the  equilibrium  reached  is  dynamic 
in  character. 

This  conception  also  explains  the  condition  that  exists 
in  many  cases  where,  on  mixing  two  substances,  no  action 
seems  to  occur,  but  in  which  reactions  are  actually  going 
on.  For  example,  sodium  chloride  and  potassium  nitrate 
are  dissolved  in  the  same  solution.  Apparently  there  is 
no  action,  but  actually  there  are  several  cases  of  equilib- 
rium. At  first  we  have  those  resulting  from  the  ionization 
of  the  two  salts  : 

NaCl       ±:Na+  +  Cl- 


162  CHEMICAL  EQUILIBRIUM 

Then  K+  ions  will  join  with  Cl~  ions,  giving  a  new  equilib- 
rium : 

K+  +    Cl-  ^±   KC1 

and  Na+  with  NOg  will  give  another : 

Na+  +    NO^  -7-^   NaNOg 

Thus  we  have  in  such  a  solution  eight  different  things 
present  at  any  instant,  and  four  cases  of  dynamic  equilib- 
rium. 

We  must  note,  however,  that  in  this  case,  as  with  the 
sealed  tubes,  no  product  can  escape  from  the  field  of  action. 
In  cases  where  one  of  the  products  does  escape,  there 
can  be  no  reverse  action,  since  some  of  the  necessary 
constituents  are  lacking. 

163.  Reactions  that   go  to  an  End.  —  If,  in  the  case  of 
the  reactions  of  copper  with  water,  the  tubes  had  been 
open,  either  the  steam  or  the  hydrogen  would  have  escaped 
from  the  field  of  action  before  it  could  have  reacted  in 
the  reverse  direction.     This  is  what  happens  if  we  reduce 
copper  oxide  by  passing  hydrogen  over  it,  or  if  we  pass 
steam  through  a  tube  containing  copper.     In  these  cases 
the  reactions  continue  in  one  direction  until  one  or  both 
of  the  constituents  have  been  entirely  converted  into  prod- 
ucts ;  such  an  action  is  said  to  go  to  an  end. 

Usually  in  practical  chemical  work  we  desire  that  our 
actions  shall  continue  until  we  obtain  as  much  of  the  prod- 
uct as  possible.  In  selecting  and  controlling  such  actions, 
the  modern  theories  of  reversibility,  equilibrium,  and  the 
effect  of  concentration  are  of  great  value. 

164.  Reactions  that  go  to  an  End  through  Volatility. — If, 
at  the  temperature  of  the  experiment,  one  of  the  products 


REACTIONS  THAT  GO   TO  AN  END  163 

of  an  action  is  a  gas,  it  will  readily  escape  from  the  react- 
ing mixture.  The  preparation  of  hydrogen  chloride  is  an 
excellent  example  of  an  action  that  goes  to  completion 
in  this  way : 

2  NaCl  +  H2SO4  -^  2  HC1  +  Na2SO4 

Sulphuric  acid  is  chosen  for  the  reason  that  its  boiling 
point  is  so  high. that  there  is  no  possibility  of  its  leaving 
the  mixture  at  the  temperature  which  will  suffice  to  drive 
off  the  hydrogen  chloride. 

This  principle  of  volatility  is  of  practical  use  in  prepar- 
ing chemical  compounds.  If  the  substance  we  desire  is 
not  itself  volatile,  we  may  still  employ  the  principle  by 
selecting  our  constituents  so  that  another  product  will  be 
volatile. 

165.  Reactions  that  go  to  an  End  through  Insolubility. — 
We  have  seen  that  solution  must  precede  ionization.  An 
insoluble  substance  does  not,  therefore,  yield  ions,  even 
though  it  may  be  floating  in  the  solvent.  Hence,  if  an 
insoluble  substance  is  formed  in  a  solvent  as  the  result  of 
a  reaction,  it  is  as  much  out  of  the  field  of  action  as  if  it 
had  left  the  mixture.  Reactions  in  which  this  happens 
go  to  an  end  just  as  they  do  if  a  volatile  product  is  formed. 
This  is  one  of  the  most  common  types  of  chemical  action. 
As  an  example,  consider  the  action  between  solutions  of 

silver  nitrate  and  sodium  chloride  :     '   . 

I     afu 

NaCl  +  AgNO3  — >-  AgCl  +  NaNO3 

Silver  chloride  is  insoluble  in  water.  It  therefore  forms 
no  ions,  and  is  out  of  the  field  of  action  when  once  formed. 
Obviously  it  cannot  play  any  part  in  causing  a  reverse 
action. 


164  CHEMICAL  EQUILIBRIUM 

166.  Reactions  that  go  to  an  End  through  Non-Ionization  — 
This  resembles  the  preceding  case.     A  substance  may  form 
which,  although  soluble,  does  not  ionize.     As  far  as  caus- 
ing a  reverse  action  is  concerned,  this  substance  is  out  of 
the  field  of  action. 

That  neutralization  actions  go  to  an  end  is  due  to  this 
fact.  The  water,  which  is  invariably  formed,  is  practically 
non-ionized. 

&/  ' 

167.  Insoluble  Substances  used  as  Tests.  —  The   test  for 
hydrochloric  acid  or  a  chloride  is  a  search  for  the  pres- 
ence of  chlorine  ions.      The  solution  of  silver  nitrate  used 
in  the  test  contains  silver  ions  : 


These  positive  silver  ions  will  encounter  negative  chlorine 
ions  if  the  solution  tested  contains  a  chloride.  Silver 
chloride  is  formed.  This  compound,  being  practically  in- 
soluble and  hence  undissociated,  separates  as  a  precipi- 
tate. Therefore  the  equation  is  : 

Ag++Cl-—  ^AgCl 

A  solution  of  potassium  chlorate  also  contains  chlorine, 
not  as  a  simple  ion,  but  as  part  of  the  ion  ClOg".  So  when 
we  mix  this  solution  with  the  silver  nitrate,  we  have  the 
ions  Ag+,  NO^",  K+,  ClOg".  Here  no  precipitation  takes 
place,  since  the  compounds,  silver  chlorate,  AgClO3,  and 
potassium  nitrate,  KNO3,  that  would  be  likely  to  form,  are 
both  soluble.  Silver  nitrate  solution,  then,  is  the  test  for 
the  chlorine  ion,  and  not  for  the  chlorine  atom. 

}/  '     -^x'yLx' 

The  test  for  a  sulphate  depends  upon  the  combination 
of  barium  ions,  Ba++  (from  the  barium  chloride  added), 
with  the  SO4  ion  of  the  sulphate.  The  barium  sul« 


LAW  OF  MASS  ACTION  165 

phate  formed  is  insoluble  and  separates  as  undissociated 
molecules.     The  equation  is  : 

Ba++  +  SO4~  —>-  BaSO4 

These  tests  furnish  good  examples  of  reactions  that  go  to 
an  end  through  insolubility. 

168.  Law  of  Mass  Action.  —  The  theory  of  moving  parti- 
cles, which  we  used  to  explain  osmotic  pressure,  can  also 
be  employed  to  make  clear  some  matters  connected  with 
ionization  and  equilibrium.  In  a  solution,  both  ions  and 
molecules  are  in  constant  movement,  and  there  are  con- 
stant collisions  between  the  particles.  As  a  result,  some 
gain  momentum  while  others  lose  it,  until  finally  the  par- 
ticles have  widely  different  velocities.  In  a  case  where 
there  exists  a  dynamic  equilibrium  like  that  shown  in  the 
equation 


the  reactions  in  the  two  directions  are  affected  by  the 
nature  of  the  collisions  which  occur.  If  a  molecule  of 
sodium  chloride  meets  with  a  violent  impact,  it  will  tend 
to  separate  into  its  ions  ;  while  two  oppositely  charged 
ions  may  meet  in  such  a  way  as  to  remain  united.  Thus 
the  reactions  in  the  two  different  directions  are  accounted 
for. 

Next  we  will  consider  an  experiment.  To  a  saturated 
solution  of  common  salt  we  add  hydrogen  chloride  gas. 
This  in  dissolving  tends  to  reach  the  equilibrium  : 

HCI  ±5:  H+  -ha- 

lt thus  gives  ions  of  a  kind  already  in  solution.  In  other 
words,  we  increase  the  concentration  of  the  chlorine  ions. 
As  an  experimental  result  of  the  addition,  we  observe 


166  CHEMICAL   EQUILIBRIUM 

that  sodium  chloride  is  precipitated  in  the  form  of  fine 
crystals. 

The  following  is  the  explanation  of  this  action.  By 
increasing  the  number  of  chlorine  ions  in  the  solution,  we 
increase  the  number  of  impacts  between  the  Na+  and  Cl~ 
ions  and  consequently  the  chance  of  forming  more  sodium 
chloride  molecules.  Since  the  solution  is  already  satu- 
rated with  these,  the  newly  formed  ones  must  precipitate. 
A  similar  result  may  be  obtained  if  we  add  a  substance, 
like  sodium  nitrate,  which  would  increase  the  concentra- 
tion of  the  Na+  ions.  Thus,  in  general,  we  can  increase 
the  speed  of  a  chemical  action  by  increasing  the  impacts 
between  the  substances  which  produce  the  action.  This 
occurs  when  the  concentration  of  even  one  of  the  sub- 
stances is  increased ;  and  in  these  cases  the  action  goes 
further  toward  completion. 

'The  law  which  states  these  generalizations  is  known  as 
the  Law  of  Mass  Action.  In  its  full  form  it  gives  the 
mathematical  relations  of  the  concentrations,  but  for  our 
purposes  we  can  put  it  in  thus:  The  speed  of  a 'chemical 
action  is  increased  in  a  given  direction  by  increasing  the  con- 
centration of  one  of  the  substances  that  produce  the  action. 

169.  Applications  of  the  Law  of  Mass  Action.  —  These  are 
of  very  great  importance,  since  the  principle,  like  those 
involved  in  ionization  and  equilibrium,  is  of  general  appli- 
cation. Chemical  actions  which  go  to  an  end  are  them- 
selves examples  of  the  operation  of  the  law.  When  a 
substance  leaves  the  field  of  action  through  its  insolu- 
bility, volatility,  or  non-ionization,  the  concentration  of 
that  substance  becomes  zero,  and  there  can  be  no  impacts 
between  it  and  another  substance  tending  to  produce  a 
reverse  action. 

But  most  actions  do  not  go  to  an  end.     Control  in  such 


APPLICATIONS  OF  THE  LAW  OF  MASS  ACTION   167 

cases  is  often  secured  through  a  knowledge  of  the  princi- 
ple of  mass  action.     Perhaps  the  most  important  examples 
are  those  involving  a  substance  that  is  almost,  but  not  l 
wholly,  insoluble.     Barium   sulphate  is  a  compound  of 
this  kind.     Therefore  the  reaction 

BaCl2  +  H2SO4—  ^  BaS04  +  2  HC1 

goes  only  approximately  to  an  end.  But  it  is  often  nec- 
essary to  precipitate  barium  as  a  sulphate  as  completely 
as  possible.  The  principle  of  mass  action  points  a  way 
to  accomplish  this,  by  the  addition  of  a  considerable  excess 
of  sulphuric  acid  when  producing  the  precipitation.  The 
concentration  of  the  SO4  ions  is  thereby  increased, 
and  the  Ba++  ions  are  brought  almost  completely  into 
reaction. 

Again,  the  activity  of  an  acid  can  be  greatly  lessened  by 
the  addition  of  a  salt  of  the  acid.  For  example,  if  to  the 
equilibrium: 

H2S04  5±:  H+  +  H+  +  SO— 

we  add  sodium  sulphate: 


we  thus  increase  the  concentration  of  the  sulphate  ions, 
and  some  of  the  hydrogen  ions  are  forced  back  into 
molecules  of  sulphuric  acid.  Since  acid  properties  are  due 
to  hydrogen  ions,  the  acid  strength  of  the  solution  in  ques- 
tion is  lessened  by  the  addition  of  the  sodium  sulphate. 
In  an  analogous  way,  a  weak  acid  becomes  practically 
inactive  in  the  presence  of  its  own  salts.  This  is  especially 
true  because  the  salts  of  weak  acids  are  much  more  highly 
ionized  than  the  acids  themselves. 


168  CHEMICAL  EQUILIBRIUM 

SUMMARY 

Chemical  actions  in  general  are  reversible.  Hence,  unless 
special  conditions  are  established,  two  substances  do  not  give 
complete  reaction  with  each  other  on  being  mixed.  A  reversal 
action  sets  in,  and  both  it  and  the  direct  action  continue  simul- 
taneously. A  state  of  dynamic  equilibrium  thus  exists. 

Where  reactions  do  not  remain  in  a  state  of  dynamic  equilib- 
rium but  do  go  to  an  end,  it  is  because  one  of  the  products  leaves 
the  field  of  action. 

This  may  happen  through  insolubility,  volatility,  or  non-ioni- 
zation. 

The  reactions  of  the  laboratory  are  chosen  so  that  they  will  go 
to  an  end  through  the  operation  of  one  of  these  principles. 

Tests  for  chlorides,  sulphates,  and  other  ions  are  good  examples 
of  action  that  go  to  an  end  through  insolubility. 

The  preparation  of  hydrogen  chloride  is  a.  good  example  of  an 
action  that  goes  to  an  end  through  volatility. 

Neutralizations  go  to  an  end  because  the  water  that  is  formed 
is  practically  non-ionized. 

The  character  of  the  equilibrium  in  a  given  chemical  action 
can  be  controlled  through'  the  Law  of  Mass  Action,  which  states : 
The  speed  of  a  chemical  reaction  is  increased  in  a  given  direction 
by  increasing  the  concentration  of  one  of  the  substances  that  pro- 
duce the  action. 

Examples  of  the  practical  application  of  the  law  of  mass  action 
are  found  in  the  facts  that  (a)  a  partly  soluble  substance  can  be 
almost  completely  precipitated  by  adding  an  excess  of  one  of  the 
ions  that  help  to  form  it,  and  (b)  that  acids  are  less  active  in  the 
presence  of  their  own  salts ;  this  is  especially  true  in  the  case  of 
weak  acids,  because  the  salts  of  these  acids  are  generally  much 
more  highly  ionized  than  the  acids  themselves. 


EXERCISES  169 

EXERCISES 

1.  What  is   meant  by  reversible   reactions  ?     Give    three 
examples. 

2.  Explain  the  meaning  of  the  word  dynamic  in  the  phrase 
dynamic  equilibrium. 

3.  Write  an  equation  to  show  that  the  ionization  of  potas- 
sium nitrate  is  a  reversible  reaction.     Under  what  conditions 
can  the  speed  be  increased  reading  from  left  to  right  ?     From 
right  to  left  ? 

4.  Write  an  equation  to  show  the  ionization  of  copper  sul- 
phate in  water  solution.     Does  this  represent  an  action  that 
goes  to  an  end  ?     Explain. 

5.  Under  what  three  conditions  do  actions  go  to  an  end  ? 
Explain. 

6.  By  reference  to  the  Table  and  Rules  for  Solubility  and 
Volatility  in  the  Appendix,  determine  which  of  the  following 
reactions  go  to  an  end,  and  which  rest  in  a  state  of  equilibrium. 
State  the  reason  in  each  case,  and  complete  the  equation  in 
case  the  reaction  goes  to  an  end  : 


HgN03  '+  KC1       —  >-  Na.SO,     +  H2SO4  —  >- 

CuS04    +sraN03—  ->-  Pb(N03)2+Na2S04—  *~ 

N^COg  +  HN03   —  >•  NH4C1      +  NaOH  —  > 

NaBr      +  H2S04   —  ^  Zn(N03)2  +  H2S04  —  *- 

BaCl2      +  CuS04  —  >-  FeCl3        +  K2S04  —  *. 

ZnS        +  H2S04  —  >-  Pb(N03)2  -f  CuCl2    —  »- 

Na^SO,  +  HC1      —  >•  FeS          +  H2S04  —  >- 

NaOH    +HN03  —  ^  NaN03     +  HC1      —  >- 

KN03     +Na2S04-^-  AgN03     +  FeCl3 

CaCl2      +Na2CO,—  >•  CaC03      +  HC1      —  >• 

7.  Write  equations  to  show  three  ways  of  making  potas- 
sium nitrate,  illustrating  each  of  the  three  ways  in  which 
reactions  may  go  to  an  end. 


170  CHEMICAL  EQUILIBRIUM 

8.  State  the  Law  of  Mass  Action. 

9.  Lead  sulphate  is  slightly  soluble  in  water.     What  could 
be  added  to  make  it  less  soluble  ?     Explain. 

10.  Is  common  salt  as  soluble  in  a  dilute  solution  of  hydro- 
chloric acid  as  it  is  in  water  ?     Explain. 

11.  Which  is  the  more  ionized  in  water  solution,  a  weak 
acid  or  its  sodium  salt  ? 

12.  If  sodium  acetate  is  present  in  a  solution  of  acetic  acid, 
what  is  the  effect  on  the  activity  of  the  acid  ? 

13.  Why  does  the  zinc  in  a  hydrogen  generator  dissolve 
less  rapidly  after  a  time,  even  .though  there  is  still  an  excess  of 
sulphuric  acid  present  ? 

14.  Hydrogen  and  the  magnetic  oxide  of  iron  react  accord- 
ing to  the  reversible  equation  : 

Fe304-  +  4  H2^±:3  Fe  +  4  H20 

How  may  the  direction  of  the  reaction  be  controlled  ?     How 
may  dynamic  equilibrium  be  established  ? 

15.  Calcium  sulphate  is  but  slightly  soluble  in  water.     Why 
is  it  difficult  to  dissolve  much  calcium  carbonate  in   dihite 
sulphuric  acid  ? 

,7      "'"• 


CHAPTER   XVIII 

SODIUM  AND  POTASSIUM  COMPOUNDS 

170.  General  Properties. —  Sodium  and  potassium  com- 
pounds may  be  studied  together  advantageously,  as  the 
corresponding  compounds  that  the  two  elements  form  are 
very  similar. 

Most  sodium  and  potassium  compounds  are  white  crys- 
talline substances ;  practically  all  of  them  are  soluble  in 
water.  With  the  exception  of  the  hydroxides,  all  of  those 
that  we  shall  study  are  salts,  possessing  in  a  marked  degree 
those  properties  which  are  characteristic  of  this  class  of 
bodies.  As  a  rule,  they  are  very  stable  compounds.  They 
are  among  our  most  common  and  useful  substances. 

Sodium  compounds  are  generally  less  soluble  in  water 
than  are  the  corresponding  potassium  compounds;  they 
are,  therefore,  not  so  satisfactory  for  certain  uses.  On  the 
other  hand,  sodium  salts  are  usually  cheaper  than  those  of 
potassium.  Moreover,  since  the  atomic  weight  of  sodium 
is  23,  while  that  of  potassium  is  39,  a  gram  of  a  sodium  salt 
contains  a  greater  number  of  molecules  than  a  gram  of 
the  corresponding  potassium  compound.  Consequently  a 
gram  of  a  sodium  salt  will  "  go  farther  "  than  a  gram  of  the 
corresponding  potassium  salt.  For  these  reasons  sodium 
compounds  are  generally  used  in  manufacturing  operations 
in  preference  to  those  of  potassium. 

PREPARATION  OF  THE  HYDROXIDES 

Of  the  methods  in  use  for  the  manufacture  of  these 
hydroxides,  two  will  be  treated.  In  describing  the  oper- 

m 


172 


SODIUM  AND  POTASSIUM  COMPOUNDS 


ations,  the  sodium  compound  will  be  taken  as  a  type  for 
both. 

171.  Electrolytic  Processes. —  We  saw  (§  74)  that  a  water 
solution  of  sodium  chloride,  on  being  decomposed  by  an 
electric  current,  gives  chlorine,  hydrogen,  and  sodium 
hydroxide  as  products : 

2  NaCl  +  2  H2O  — »-  2  NaOH  +  C12  +  H2 

The  products  of  this  reaction  must  not  be  allowed  to  mix 
during  the  electrolysis,  lest  other  and  mor'e  complicated 
changes  take  place. 


^Mercury 


Eccentric 


FIG.  41.  —  ELECTROLYTIC  PREPARATION  OF  SODIUM  HYDROXIDE. 

(1)  The  Castner  process  is  one  of  the  earlier  electrolytic 
methods  that  still  ranks  high  for  the  production  of  pure 
sodium  hydroxide.  The  apparatus  (Fig.  41)  consists  of 
a  stone  cell,  about  4  feet  square  and  6  inches  deep,  divided 
into  three  compartments.  The  end  compartments  contain 
a  concentrated  solution  of  salt.  The  middle  compartment 
at  first  contains  a  dilute  solution  of  sodium  hydroxide.  A 
layer  of  mercury  covers  the  bottom  of  the  cell,  passing 
under  the  partitions,  and  keeps  the  solutions  in  adjacent 
compartments  from  mixing.  The  mercury  is  made  to  flow 


Hamilton  Young  Castner 

(1857-1899)  was  born  in 
Brooklyn,  N.Y.  His  first  suc- 
cess was  in  the  reduction  of 
the  price  of  aluminum,  then 
obtainable  only  by  the  use  of 
sodium,  from  $10  to  $1  per 
pound,  by  cheapening  the  pro- 
duction of  sodium.  But  this 
process  was  destined  to  be 
superseded  by  Hall's  still 
cheaper  electrolytic  method. 
Castner's  most  important  in- 
vention is  the  electrolytic 
method  by  which  we  get  pure 
sodium  hydroxide  directly  c 
from  common  s~lt. 


Ernest  Solvay  was  born  in 

Belgium  in  1839  and  still  lives 
in  Brussels.  He  made  prac- 
tical a  process  for  obtaining  the 
carbonates  of  sodium  directly 
from  common  salt  by  a  precipi- 
tation method.  His  process  is 
the  only  one  used  in  this 
country.  Solvay  has  received 
many  honors  and  great  wealth 
as  a  result  of  his  discovery. 
He  has  been  prominent  in  the 
political  life  of  his  country  and 
has  been  a  member  of  the 
Belgian  Senate. 


ELECTROLYTIC   SODIUM  HYDROXIDE  173 

backward  and  forward  by  rocking  the  apparatus  by  means 
of  an  eccentric,  which  causes  one  end  of  the  cell  to  be 
raised  and  then  lowered  half  an  inch.  Carbon  anodes  are 
placed  in  the  end  compartments  and  an  iron  cathode  in 
the  middle  compartment. 

The  current  passes  from  the  anode  through  the  salt 
solution  to  the  mercury,  and  then  from  the  .mercury 
through  the  sodium  hydroxide  solution  to  the  iron  cathode. 
This  makes  the  mercury  negative  relative  to  the  carbon 
anodes,  and  positive  relative  to  the  iron  cathode.  Chlo- 
rine ions  pass  to  the  anodes,  where  chlorine  gas  is  liberated 
and  drawn  from  the  apparatus.  The  sodium  ions  pass  to 
the  mercury  and  the  sodium  is  carried  with  the  mercury 
to  the  middle  compartment.  Here  sodium  ions  pass  to 
the  iron  cathode,  lose  their  electric  charges,  and  at  once 
react  with  the  water.  Sodium  hydroxide  and  hydrogen 
result  from  the  reaction. 

In  this  way  a  solution  containing  about  27  %  of  sodium 
hydroxide  is  obtained.  The  solution  is  drawn  off,  the 
water  evaporated,  and  the  sodium  hydroxide  obtained 
pure  as  a  white  solid.  This  is  melted  and  cast  into  sticks 
or  run  into  iron  drums.  The  chlorine  which  is  obtained 
as  a  by-product  is  used  to  make  bleaching  powder.  The 
hydrogen  -is  not  utilized. 

(2)  Large  quantities  of  sodium  hydroxide  that  is  suffi- 
ciently pure  for  technical  purposes  are  made  by  the  elec- 
trolysis of  solutions  of  sodium  chloride  in  vessels  .arranged 
so  that  the  anode  chamber  is  separated  from  the  cathode 
chamber  by  a  porous  partition  or  diaphragm.  A  concen- 
trated solution  of  salt  is  fed  to  the  compartment  containing 
the  anode  and  the  solution  of  sodium  hydroxide  formed  at 
the  cathode  is  drawn  off  continually.  The  chlorine  which 
is  obtained  as  a  by-product  is  either  liquefied  and  shipped  in 
that  form  for  use,  or  is  utilized  for  the  manufacture  of 


174         SODIUM  AND  POTASSIUM  COMPOUNDS 

chlorine  compounds  such  as  bleaching  powder  and  carbon 
tetrachloride. 

172.  Lye  Process. —  Calcium  hydroxide,  Ca(OH)2,  ordi- 
nary slaked  lime,  is  made  from  calcium  oxide,  CaO,  un- 
slaked lime,  by  adding  water : 

CaO  +  H2O  — ^  Ca  (OH)2 

Calcium  hydroxide  is  slightly  soluble  in  water.  If  a  solu- 
tion of  it  is  boiled  with  sodium  carbonate,  Na2CO3,  the 
following  reaction  occurs : 

Na2CO3  +  Ca(OH)2  -^-  2  NaOH  +  CaCO8 

The  calcium  carbonate,  CaCO3,  formed  is  insoluble.  It 
is  this  fact  that  makes  the  action  go  to  an  end.  The 
solution  of  sodium  hydroxide  is  separated  from  the  pre- 
cipitated calcium  carbonate  and  evaporated  to  dry  ness. 

173.  Properties  of  the  Hydroxides.  —  The  hydroxides  are 
very   strong   bases.     As    we    have    seen,  they  neutralize 
acids,  forming  salts  and  water.     These  bases  have  such 
a  corrosive  action  on  animal  and  vegetable  matter  that 
they  are  called  caustic  alkalies.     Solutions  of  either  sodium 
hydroxide   or  potassium   hydroxide   readily  dissolve  silk 
and  wool.     Dilute  solutions  of  these  alkalies  have  little 
effect  on  cotton,  but  warm  concentrated  solutions  react 
with  the  cotton  fiber.     This  action  is  the  first  step  in  the 
manufacture  of  mercerized  cotton.     Glass  is  attacked  by 
these  hydroxides ;    and  although  the  action  is  somewhat 
slow,  a  solution  of   either   hydroxide  on  standing  in  a 
glass   bottle   becomes  quite  impure.     Both   sodium   and 
potassium  hydroxides  are  very  deliquescent  substances. 

174.  Uses.  —  Sodium  hydroxide,  caustic  soda,  is  manu- 
factured in  enormous  quantities  for  use  in  soap  making. 


SOURCES  OF  SODIUM  CHLORIDE  175 

It  is  also  used  in  making  bleaching  solutions,  and  in 
numerous  other  operations.  Potassium  hydroxide,  caustic 
potash,  is  not  so  extensively  used  in  manufacturing  opera- 
tions. It  is  used  to  make  other  compounds  of  potassium, 
and  in  the  preparation  of  some  soaps. 

175.   Sodium  Peroxide.  —  This    compound   is   made    by 
heating  slices  of  sodium  in  air  freed  from  carbon  dioxide: 


The  temperature  for  the  reaction  must  be  kept  between 
300°  C.  and  400°  C. 

Sodium  peroxide  reacts  violently  with  water,  producing 
sodium  hydroxide  and  oxygen  : 

2  Na2O2  +  2  H26  —  >-  4  NaOH  +  62 

When  the  reaction  is  carefully  regulated,  it  is  a  most  con- 
venient laboratory  method  for  making  small  quantities  of 
oxygen.  Sodium  peroxide  should  never  be  left  on  paper 
or  other  combustible  material,  as  the  heat  of  reaction  with 
moisture  may  cause  a  blaze.  Sodium  peroxide  is  useful 
for  making  solutions  of  hydrogen  peroxide  for  laboratory 
use,  by  sifting  the  powder  into  very  dilute  acid  solutions  : 

Na^  +  2  HC1  —  >-  H2O2  +  2  NaCl 

The  use  of  sodium  peroxide  as  an  oxidizing  and  bleach- 
ing agent  is  increasing. 

176.  Sources  of  Sodium  Chloride.  —  Sodium  chloride, 
NaCl,  common  salt,  is  the  most  abundant  sodium  com- 
pound found  in  nature.  Rock  salt,  or  halite  (Fig.  42),  is 
found  in  many  countries,  but  the  largest  deposits  are  those 
in  New  York,  Louisiana,  Austria,  Germany,  and  Spain. 
Often  in  these  beds  the  salt  is  of  such  purity  that  it  has 
only  to  be  mined  and  crushed  to  be  ready  for  use. 


176         SODIUM  AND  POTASSIUM  COMPOUNDS 


Much  of  the  salt  in  this  country  is  obtained  from  salt 
wells  in  New  York,  Michigan,  Ohio,  and  other   states. 

Several  borings  are  made  and 
water  sent  down  some  of  them 
(Fig.  43,  a)  to  the  salt  bed. 
There  brine  is  formed  and 
forced,  or  pumped,  through 
other  borings  (6)  to  the  sur- 
face. The  earthy  impurities 
in  the  brine  settle,  and  then 
it  is  evaporated,  usually  under 
reduced  pressure.  A  fairly 
pure  salt  is  thus  obtained. 

The  total  amount  of  salt 
found  in  deposits,  however,  is 
insignificant  compared  with 
the  quantity  contained  in  the 
seas  and  oceans.  The  percentage  of  salt  in  sea  water  is  small, 
yet  it  has  been  computed  that  the  total  quantity  in  the  sea 
is  36,000,000,000,000,000  tons.  The  percentage  of  salt  is 


FIG.  42.  —  ROCK  SALT. 


FIG.  43.  —  DIAGRAM  OF  SALT  WELLS. 

a,  works  at  which  water  is  pumped  to  salt  strata ;  b,  works  at  which  brine 
is  pumped  to  surface. 


SOURCES   OF  SODIUM  CHLORIDE  177 

not  uniform  for  all  seas  and  oceans.  These  variations  de- 
pend upon  the  ratio  existing  between  the  amount  of  water 
delivered  by  rivers  to  a  sea  and  the  amount  lost  by  evapora- 


Copyright  by  Underwood  and  Underwood. 

FIG.  44.  —  COLLECTING  SALT  AFTER  EVAPORATION  IN  RUSSIAN  SALT  FIELDS 

tion.  Thus,  in  the  Baltic  Sea,  the  inflow  of  river  water, 
which  contains  much  less  salt  than  sea  water,  exceeds  the 
loss  by  evaporation.  Hence  the  water  of  the  Baltic  is 
relatively  fresh.  In  the  Dead  Sea  the  reverse  conditions 


178         SODIUM  AND  POTASSIUM   COMPOUNDS 

prevail ;  evaporation  exceeds  the  inflow,  and  a  solution  ap- 
proaching saturation  has  resulted.     The  average  amounts 
of  salts  contained  in  one  hundred  parts  of  sea  water  are  : 
Dead  Sea       .     .22.0  parts     Atlantic  Ocean     .  3.6  parts 
Mediterranean  .     3.8  parts     Baltic     ....   0.5  part 

177.  Extraction  of  Salt  from  Sea  Water.  —  The  method  em- 
ployed for  getting  salt  from  sea  water  depends  upon  the 
climate.     In  warm  countries  the  sea  water  is  evaporated 
by  the  sun's  heat  in  shallow  basins  (Fig.  44).     The  salt  that 
thus   crystallizes   is   not   very    pure.      In  cold  countries 
like  northern  Russia,  sea  water  is  allowed  to  freeze  in  flat 
basins.     The  coating  of  ice,  which  contains  very   little 
salt,  is  removed,  and  the  process  repeated  till  a  concen- 
trated brine  is  obtained,  'which  it  will  pay  to  evaporate  by 
artificial  heat. 

178.  Purification  of  Salt.  —  Common  salt  contains  several 
impurities.     The  principal  impurity  is  magnesium  chlo- 
ride, a  deliquescent  substance  which  causes  ordinary  salt 
to   cake.     To   get  the  pure   sodium    chloride,   hydrogen 
chloride  is  passed  into  a  saturated  brine,  or  concentrated 
hydrochloric  acid  is  added.     Pure  salt  separates,  because 
it  is  less  soluble  in  a  solution  of  hydrochloric  acid  than  in 
water  (§  168). 

179.  Properties  and  Uses  of  Sodium   Chloride.  —  Sodium 
chloride  crystallizes  in  transparent  cubes.    Generally  these 
cubes  arrange  themselves  in  four-sided,  hollow  pyramids, 
known   as   hopper   crystals    (Fig.    45).     Water   is   often 
mechanically  included  in  the  crystals  when  salt  separates 
from  solution.     When  such   crystals  are  heated,  the  in- 
closed water,  being  converted  into  steam,  is  violently  ex- 
pelled with  a  crackling  noise  and  the  flying  about  of  small 


POTASSIUM  CHLORIDE 


179 


particles  of  salt.  This  action  is  known  as  decrepitation. 
Sodium  chloride  is  but  slightly  more  soluble  in  hot  water 
than  in  cold.  It  vaporizes  slowly  at  a  red  heat. 

Sodium   chloride  is   typical  of  one  of  the  three  great 
classes  of  chemical  compounds.     It  was  the  first  represen- 
tative of  its  class  to  become  familiar  to  man.     Other  com- 
pounds with  properties  similar  to  com- 
mon salt  became  known  as  salts.     For 
a    long    time    the    term    salt    meant    a 
white  substance  soluble  in  water,  with 
a  taste  resembling  common  salt.     Many 
compounds  now  known  as  salts  possess 
neither   of   these   properties.     A  water 
solution  of  a  salt,  like  sodium  chloride, 
does    not  change    the    color   of   litmus. 
Like  most  salts,  sodium  chloride  is  com- 
posed of  a  metallic  element  and  a  non- 
metallic  constitutent. 

Salt  is  indispensable  as  a  food  for 
the  higher  animals.  It  furnishes  the 
chlorine  needed  for  the  hydrochloric 
acid  in  the  gastric  juice.  Tons  of  com- 
mon salt  are  used  every  year  in  the 
preparation  of  sodium  carbonate  and 
sodium  hydroxide.  Enormous  quan- 
tities of  salt  are  consumed  in  refriger- 
ation and  in  curing  meat  and  fish. 


FIG.  45. 


180.  Potassium  Chloride.  —  The  chloride  of  potassium, 
KC1,  is  also  found  in  sea  water,  but  in  smaller  quantities 
than  sodium  chloride.  Its  most  important  source  is  the 
mineral  deposits  at  Stassfurt,  Germany. 

The  properties  of  potassium  chloride  are  similar  to  those 
of  sodium  chloride,  but  the  potassium  compound  is  more 


180         SODIUM  AND  POTASSIUM  COMPOUNDS 

soluble  in  water.  The  chloride  is  used  in  the  manufacture 
of  other  potassium  compounds,  particularly  the  nitrate  and 
the  chlorate.  K  I 

Potassium  chloride  is  extensively  used  in  the  manufacture 
of  fertilizers,  because  it  is  the  cheapest  compound  of  potas- 
sium, an  element  essential  to  plant  life. 

181.  Occurrence  and  Preparation  of  the  Carbonates  (Na2C03, 
KgCOg).  —  These  important  compounds  occur  only  to  a 
very  limited  extent  in  nature.  The  ashes  of  land  plants 
contain  potassium  carbonate,  and  the  ashes  of  sea  plants 
both  sodium  and  potassium  carbonates. 

The  most  important  process  for  the  manufacture  of 
sodium  carbonate  and  sodium  bicarbonate  is  the  Solvay 
process. 

The  gas  ammonia,  NH3,  is  the  anhydride  (§  210)  of  the 
base  ammonium  hydroxide,  NH4OH;  in  other  words,  it 
will  unite  with  water  to  form  ammonium  hydroxide : 

(1)  NH3  +  H20— -^NH4OH 

Carbon  dioxide  (carbonic  anhydride)  unites  with  water 
to  form  an  acid,  carbonic  acid,  H2CO3 : 

(2)  C02  +  H20-^H2C03 

When  ammonium  hydroxide  is  brought  in  contact  with 
an  excess  of  carbonic  acid,  all  of  the  OH"  ions  of  the  base 
unite  with  H+  ions  from  the  acid  and  the  solution  will 
contain  ammonium  hydrogen  carbonate  or  ammonium  bi- 
carbonate : 

(3)  NH4OH  +  H2C03 — ^H20  +  NH4HCO3 

If  a  solution  of  ammonium  bicarbonate  comes  in  con- 
tact with  a  solution  of  sodium  chloride,  sodium  bicarbonate 


&'&r  "*-  f+ 

PREPARATION  OF  CARBONATES  181 

will  separate,  because  it  is  insoluble  under  the  conditions 
of  the  experiment  : 


(4)  NH4HC03  +  NaCl—  ^NaHC03  +  NH4C1 

The  above  considerations  may  aid  in  obtaining  equation 
(5),  generally  written  to  represent  the  Solvay  process. 
Equation  (5)  is  the  sum  of  equations  (1),  (2),  (3),  and  (4). 

(5)  NaCl  +  H2O  +  CO2  +  NH3—  ^NaHCO3  +  NH4C1 


In  practice  the  operation  is  carried  out  by  saturating  a 
concentrated  brine  with  ammonia  and  then  passing  carbon 
dioxide  into  this  mixture  under  pressure. 

The  sodium  bicarbonate  is  separated  by  filtration  and 
purified.  The  impure  sodium  bicarbonate  remaining  after 
the  filtration  of  the  liquid  is  washed  with  water,  dried,  and 
then  heated  to  drive  off  volatile  impurities  and  to  convert 
it  into  pure  sodium  carbonate  : 

2  NaHCOg—  *-Na,C08  +  H2O  +  CO2 

The  pure  sodium  carbonate  thus  obtained  may  be 
(a)  placed  on  the  market  as  anhydrous  sodium  carbonate 
(soda  ash)  ;   (6)  crystallized  from  water  solution  and  sold 
as  washing  soda,  Na2CO3  •  10  H2O  j  (<?)  reconverted  into 
pure  sodium  bicarbonate,  baking  soda,  NaHCO3  : 

Na2C03  +  H20  +  CO2—  ^2  NaHCO3 

It  is  a  matter  of  great  importance  to  produce  sodium 
carbonate  at  low  cost.  For  this  reason  the  above  reactions 
are  carried  out  so  that  the  by-products  are  utilized.  The 
ammonium  chloride  is  used  to  furnish  ammonia  to  saturate 
a  fresh  supply  of  brine.  The  carbon  dioxide  that  is  given 
off  in  decomposing  sodium  bicarbonate  furnishes  part  of 
the  supply  of  that  gas  needed  in  the  first  step  of  the  oper- 
ation. 


182         SODIUM  AND  POTASSIUM   COMPOUNDS 

182.  Uses  of  the  Carbonates.  —  Two  uses  of  the  carbon- 
ates of    sodium    have  been  implied   in  the  names  wash- 
ing soda  and  baking  soda.     The  former  has^  in  a  modified 
way,  the  properties  of  sodium   hydroxide.     It   is   often 
called  "soda."     In  the  refining  of  petroleum,  sodium  car- 
bonate is  used  to  neutralize  sulphuric  acid.     It  dissolves 
many  substances,  especially  oils  or  fats,  and  hence  it  is  an 
excellent  cleansing  substance.     It  is  usually  an  important 
constituent  of  cleaning  powders.     Both  washing  soda  and 
baking  soda  liberate  carbon  dioxide  when  treated  with 
acids  : 

Na2CO3  +  2  HC1  —  >-  2  NaCl  +  H2O  +  CO2 
NaHC03  +  HC1  —  ->-  NaCl  +  H2O  +  CO2 

Taking  into  consideration  the  molecular  weights,  we  see 
from  these  equations  that  for  equal  weights  of  the  carbon- 
ates, baking  soda  furnishes  the  greater  amount  of  carbon 
dioxide.  It  is  consequently  preferred  for  those  uses,  as  in 
baking  powder,  in  which  the  liberation  of  carbon  dioxide 
is  required. 

Sodium  bicarbonate  is  used  in  chemical  fire  extin- 
guishers, is  an  important  constituent  of  baking  powders, 
and  is  used  in  the  manufacture  of  effervescent,  salts. 

183.  Hydrolysis.  —  Water  solutions  of  sodium  carbonate 
and  of  sodium  bicarbonate  are  not  neutral,  but  alkaline. 
This   depends  upon    the  slight   dissociation   of  water,  a 
condition  which  was  not  taken  into  account  in  the  discus- 
sion of  the  dissociation  of  compounds: 


In  most  cases  the  few  hydrogen  and  hydroxyl  ions  from 
the  dissociation  of  the  solvent  have  little  effect,  but  their 
presence  must  be  reckoned  with  when  the  solution  con- 
tains a  compound  which  is  but  slightly  more  dissociated 


HYDROLYSIS  183 

than  water  itself,  e.g.  carbonic  acid,  H2CO3.  When  sodium 
carbonate,  one  of  the  salts  of  this  acid,  dissolves,  it  largely 
dissociates  into  Na+  ions  and  CO3  ions.  All  of  the 
hydrogen  ions  from  the  water,  however,  cannot  remain  as 
such  in  the  presence  of  CO3  ions,  because  undissociated 
carbonic  acid  will  be  formed  : 

2  (H+)  +  CO,"  — ^  HaC08 

The  withdrawal  of  the  hydrogen  ions  to  form  an  undisso- 
ciated compound  disturbs  the  equilibrium  of  water  with 
its  ions,  and  a  few  molecules  of  water  will  have  to  dissociate 
in  order  to  restore  it.  Most  of  the  newly  formed  hydrogen 
ions  likewise  pass  into  the  undissociated  carbonic  acid. 
This  process  of  dissociation  and  combination  is  repeated 
till  an  equilibrium  is  established.  It  must  be  remembered, 
however,  that  the  progressive  dissociation  of  water  gave 
OH~  ions  as  well  as  H+  ions.  These  hydroxyl  ions  have 
little  tendency  to  combine  with  the  Na+  ions  to  form 
undissociated  sodium  hydroxide,  but  simply  remain  in 
solution  as  ions  of  this  strongly  dissociated  compound. 
There  are  enough  of  these  hydroxyl  ions  to  give  the  blue 
reaction  with  litmus. 

All  these  changes  may  be  expressed  by  the  equation : 
2  (Na+)  +  COj  -  +  2  (H+)  +  2  (OH~)  — *- 

H2CO3+2  (Na+)  +  2  (OH') 

Such  a  change,  involving  water,  is  known  as  hydrolysis, 
and  is  the  reverse  of  neutralization.  Carbonic  acid,  be- 
ing but  slightly  dissociated  in  water  solution,  is  a  weak 
acid,  while  sodium  hydroxide  is  a  strongly  dissociated 
base.  Hence  sodium  carbonate  is  a  salt  formed  by  a  weak 
acid  with  a  strong  base.  Such  salts  undergo  hydrolysis 
when  dissolved  in  water,  and  their  solutions  give^alkaUne 
reactions.  Sodium  acetate,  sodium  cyanide,  and  sodium 
sulphide  are  salts  of  this  character. 


184         SODIUM  AND  POTASSIUM  COMPOUNDS 

Some  salts,  as  copper  sulphate,  give  an  acid  reaction  in 
water  solution.     This  is  also  a  case  of  hydrolysis  : 


Cu++  +  SOj  -  +  2  (H+)  +  2 

Cu(OH)2  +  2  (H+)  +  SO^  - 

A  detailed  explanation  would  show  that  nearly  all  the 
OH  ions  from  the  dissociation  of  the  water  combine 
with  the  Cu++  ions  to  form  undissociated  copper  hydrox- 
ide, a  very  weak  base.  The  hydrogen  ions  from  the  water 
are  present  at  the  end  of  the  hydrolysis  as  ions  of  the 
strongly  dissociated  sulphuric  acid.  These  hydrogen  ions 
give  the  red  .effect  with  litmus,  and  the  acid  reaction  of  a 
solution  of  copper  sulphate  is  accounted  for. 

The  acid  reaction  of  solutions  of  such  stilts,  formed  Inj  a 
weak  base  with  a  strong  acid,  is  due  to  hydrolysis.  Zinc 
sulphate,  aluminum  sulphate,  and  ferric  chloride  are  salts 
of  this  kind. 

Salts  formed  by  strong  acids  with  strong  bases  are  not 
subject  to  hydrolysis,  since  their  ions  have  little  tendency 
to  combine  with  the  H+  and  OH~  ions  of  water  to  form 
undissociated  compounds.  The  solutions  of  such  salts  are 
neutral.  Sodium  chloride  and  potassium  nitrate  belong 
to  this  class. 

In  general,  hydrolysis  is  possible  with  a  salt  only  when 
either  the  acid  or  base  forming  it,  or  both,  are  weak. 

184.  Occurrence  of  the  Nitrates  (NaN03,  KN03).  —  Both 
sodium  and  potassium  nitrates  occur  in  small  quantities  in 
the  soil.  They  are  formed  by  nitrogenous  organic  matter 
decaying  in  contact  with  soluble  sodium  or  potassium  com- 
pounds. 

Deposits  of  sodium  nitrate,  covering  an  area  of  over  four 
hundred  square  miles,  are  found  in  desert  regions  along 
the  western  coast  of  South  America.  These  beds  lie  near 


THE  NITRATES  185 

the  boundary  lines  of  Peru,  Chile,  and  Bolivia  and  have 
been  the  cause  of  many  disputes  between  these  countries. 
The  boundary  lines  have  now  been  so  adjusted  that  Chile 
owns  the  greater  portion  of  these  extremely  valuable  de- 
posits. The  crude  nitrate  is  obtained  by  crushing  the 
loose,  rocky  material  of  the  beds  and  boiling  it  in  water. 
The  liquor  containing  the  nitrate  is  run  off  and  allowed 
to  crystallize.  The  product,  crude  Chile  saltpeter,  con- 
tains 94  %  to  98  %  of  sodium  nitrate.  A  purer  quality  is 
obtained  by  recrystallization. 

T9 l- J  -  " 

185.  Manufacture  of  Potassium  Nitrate. — Most  "of  the 
potassium  nitrate  (niter)  now  used  is  prepared,  from  sodium    i//c 
nitrate.     The   potassium   compound  is  made   by  mixing 
.hot,  concentrated  solutions  of  sodium  nitrate  and  potas-^' 

sium  chloride.     The  equation  for  the  reaction  is : 

KC1  +  NaNOg  — >-  KNOg  +  NaCl 

On  evaporation  the  boiling  mixture  first  deposits  common 
salt,  since  this  substance  is  less  soluble  in  boiling  water 
than  is  potassium  nitrate.  On  cooling  the  solution,  119 w- 
ever,  the  potassium  nitrate  crystallizes  out,  because  it  is 
far  less  soluble  in  cold  than  in  hot  water.  A  purer  quality 
of  potassium  nitrate  can  be  obtained  by  recrystallization. 

186.  Properties  of  the  Nitrates.  —  Sodium  and  potassium 
nitrates  are  white,  soluble  salts.     Sodium  nitrate  differs 
from  the  potassium  compound  in  crystalline  form  and  in 
being  hygroscopic.     Both  nitrates  give  off  oxygen  when 
heated,  and  leave  compounds,  known  as  nitrites,  contain- 
ing less  oxygen. 

187.  Uses.  —  The   principal   use    of    potassium    nitrate 
(ordinary  saltpeter)  is  in  the  manufacture  of  black  gun- 
powder.    Potassium  nitrate  is  also  used  to  preserve  meat, 


186          SODIUM  AND  POTASSIUM  COMPOUNDS 

and  corned  beef  owes  its  red  color  to  this  treatment.  The 
cheaper  sodium  nitrate  has  replaced  potassium  nitrate  in 
the  manufacture  of  nitric  acid  and  its  derivatives.  Chile 
saltpeter  is  also  used  as  a  fertilizer,  and  in  the  manufac- 
ture of  sodium  nitrite,  a  most  important  substance  in  the 
manufacture  of  aniline  dyes. 

188.  Sodium  Nitrite  is  a  by-product  obtained  in  the  man- 
ufacture of  a  fine  quality  of  red  lead  by  the  addition  of 
molten  lead  to  sodium  nitrate : 

3  Pb  +  4  NaN03  — ^  Pb3O4  +  4  NaNO2 

SUMMARY 

The  hydroxides  of  sodium  and  potassium  are  prepared  by  the 
electrolysis  of  solutions  of  the  chlorides,  and  by  the  reaction  of  the 
carbonates  with  slaked  lime. 

Sodium  peroxide  is  made  by  burning  sodium  in  air.  It  is  used 
as  an  oxidizing  agent. 

The  chlorides  of  these  two  metals  occur  in  nature. 

They  are  typical  salts.  They  have  a  saline  taste,  are  neutral, 
and  result  from  the  action  of  the  corresponding  acid  and  base. 

The  chlorides  are  used  in  the  preparation  of  other  sodium  and 
potassium  compounds. 

The  carbonates  occur  in  plant  ashes. 

They  are  commercially  prepared  by  the  decomposition  of  the 
bicarbonates  by  heat. 

The  carbonates  are  used  in  the  preparation  of  soaps,  washing 
powders,  glass,  and  in  making  other  compounds. 

The  bicarbonates  are  made  commercially  by  the  action  of  carbon 
dioxide  with  ammoniacal  solutions  of  the  chlorides. 

They  are  only  slightly  soluble  and  are  less  corrosive  than  the 
carbonates. 


EXERCISES  187 

Sodium  bicarbonate  is  a  constituent  of  all  baking  powders  and  is 
used  in  chemical  fire  extinguishers. 

Sodium  nitrate  is  obtained  from  Chile.  Potassium  nitrate  is 
formed  by  the  reaction  of  potassium  chloride  with  sodium  nitrate. 

Sodium  nitrate  is  used  to  prepare  potassium  nitrate,  also  as  a 
fertilizer  and  as  a  source  of  nitric  acid.  Potassium  nitrate  is  used 
in  gunpowder. 

EXERCISES 

1.  How  could  you  show   that  there  are  potassium  com- 
pounds in  plants  ?     K^iA^  [,cA    ft  0  , 

2.  Describe  one  process  used  for  the  preparation  of  sodium 
hydroxide.     ^  [••   ^  jtjL  ;  '<uu^ 

3.  Compare  the  profferties  of  sodium  hydroxide  with  those 
of  potassium  hydroxide.    K  0  \*t~  t/^^cr^t^  *&V~t&J'*Qt~  « 

4.  What  oxide  is  made  by  burning  sodium  in  air  ?     What 
is  this  oxide  used  for  ?  -  -*.  QA/&1 

5.  How  many  liters  of  oxygen  could  be  obtained  from  30 
grams  of  sodium  peroxide  by  its  reaction  with  water  ? 

6.  Cite  cases  to  show  that  salt  is  of  great  importance  to 
chemical  industries. 

7.  Mention  three  ways  in  which  salt  is  obtained. 

8.  Why  does  table  salt  "  cake  "  ? 

9.  How  could  pure  sodium  chloride  be  obtained  from  salt  ? 

10.  Why  was  sodium  carbonate  obtained  from  the  ashes  of 
sea  plants  and  not  from  the  water  directly  ? 

11.  Write  the  equations  for  the  preparation  of  sodium  car- 
bonate by  the  Solvay  process. 

12.  In  getting  the  normal  carbonate,  in  the  Solvay  process, 
why  do  we  have  to  get  the  bicarbonate  first  and  then  decom- 
pose it  ? 

13.  What  advantage  has  baking  soda  over  potassium  bicar- 
bonate ? 


188         SODIUM  AND  POTASSIUM  COMPOUNDS 

14.  Equal  weights  being  taken,  which  will  neutralize  the 
larger  quantity  of  acid,  sodium  hydroxide  or  potassium  hy- 
droxide ?     Sodium  carbonate  or  bicarbonate  ? 

15.  -Why  is  "soda"  used  in  cleaning? 

16.  What  objection  is  there  to  using  solutions  of  washing 
soda  to  cleanse  woolen  goods  ? 

17.  How  could  you  distinguish  chemically  between  washing 
soda  and  baking  soda  ? 

18.  Would  a  water  solution  of  sodium  bicarbonate  give  an 
alkaline  or  an  acid  reaction  ?     Explain. 

19.  How   could   you   tell    potassium    nitrate    from    sodium 
nitrate  ? 

20.  How  are  the  nitrates  produced  in  nature  ? 

21.  Why  can  potassium  nitrate  be  obtained  by  a  reaction  be- 
tween potassium  chloride  and  sodium  nitrate  ? 

22.  How  many  pounds  of  sodium  nitrite  could  be  obtained 
from  200  pounds  of  sodium  nitrate  ? 


CHAPTER   XIX 


SULPHUR  AND  SULPHIDES 

SULPHUR 

189.  Occurrence.  —  Sulphur   is  found   in  nature  either 
free  or  in  combination  with  other  elements.     In  the  un- 
combined  or  native  state  it  is  found  in  volcanic  regions. 
The  most  extensive  deposits  of  native  sulphur  are  the 
Louisiana  and  Texas  beds,  where  the  sulphur  is  found  500 
feet  below  the  surface. 

Sulphur  is  found  combined  with 
many  different  metals,  as  sulphides; 
those  of  iron,  copper,  lead,  and  zinc  are 
the  more  abundant.  The  sulphates  of 
a  few  metals  are  found  in  considerable 
quantities. 

190.  Extraction,  Frasch  Method.  —  On 

account  of  the  overlying  beds  of  quick- 
sands, several  companies  failed  to  ex- 
tract profitably  the  sulphur  from  the 
Louisiana  deposits.  It  remained  for 
Herman  Frasch,  an  American  chemist, 
to  devise-  a  most  ingenious  and  scien- 
•  tine  method. 

In  the  Frasch  process,  a  hole  is  drilled 
and  piped  down  through  the  500  feet 
of  overlying  deposits  to  the  bottom  of 
the  sulphur  bed,  which  is  often  200  feet  more.     Inside 
the  large  pipe  casing  of  the  hole  for  the  entire  distance  is 

189 


FIG.  46. 


190 


SULPHUR  AND  SULPHIDES 


a  6-inch  pipe,  and  inside  this  a  3-inch  pipe,  which  in  turn 
surrounds  a  1-inch  pipe  (Fig.  46).  Through  the  6-inch 
pipe,  water  heated  to  167°  C.  under  a  pressure  of  100 
pounds  is  forced  down  the  well  to  melt  the  sulphur  below. 
Hot,  compressed  air,  coming  down  through  the  1-inch 
pipe,  mingles  with  the  liquid  sulphur  and  reduces  the 

specific  gravity  of 
the  liquid,  so  that 
it  can  be  raised  to 
the  surface. 

The  combined 
pressure  of  the  col- 
umn of  hot  water 
and  the  compressed 
air  pumped  in, 
raises  the  sulphur 
above  the  surface 
through  the  3-inch 
pipe.  Strainers  at 
the  bottom  prevent 
earthy  material 
from  being  driven 
upward.  On  reach- 
ing the  surface,  the 
melted  sulphur  is 
run  into  huge  bins 
60  feet  high,  made 
of  rough  boards  (Fig.  47).  The  sulphur  soon  cools, 
forming  an  enormous  block  of  solid  sulphur  of  remark- 
able purity  (99%).  Some  of  the  blocks  contain  100,000 
tons.  The  block  is  broken  up  by  blasting  (Fig.  48) 
and  loaded  on  cars  by  steam  shovels.  The  hole  at  the 
right  of  the  center  of  the  picture  shows  where  liquid 
sulphur  ran  out  when  the  surrounding  solid  mass  was 


FIG.   47.  —  STREAM    OF   SULPHUR    DISCHARGING 
INTO  BIN. 


Herman  Frasch  (1852-1914),  a  native  of  Wlirtemberg,  took  up 
the  practice  of  pharmacy  at  sixteen.  We  find  him,  a  few  years 
after  coming  to  America,  establishing  an  industrial  laboratory  of 
his  own.  He  secured  patents  on  a  wide  variety  of  industrial  pro- 
cesses, the  most  valuable  relating  to  the  refining  of  petroleum  and 
to  sulphur.  His  desulphurization  of  the  Ohio  and  Canadian  petro- 
leums made  these  low-grade  oils  valuable.  Where  many  had 
failed,  he,  after  ten  years  of  labor,  developed  a  profitable  method 
for  extracting  the  Louisiana  sulphur.  He  was  awarded  the  Perkin 
Medal  in  1912. 


PURIFICATION  OF  CRUDE  SULPHUR 


191 


blasted    away.      This    sulphur    not    only   supplies    the 
American  market,  but  is  shipped  to  Europe  as  well. 


FIG.  48.  —  REMOVAL  OF  SULPHUR  FROM  BIN  AFTER  BLASTING. 

191.  Extraction,  Sicilian  Method.  ^— The  rocky  material 
containing  the  sulphur  produced  in  volcanoes  is  heaped 
into  piles  which  are  then  covered  with  spent  ore.     Suffi- 
cient air  is  admitted  to  the  pile  to  burn  a  small  portion 
of  the  sulphur.     The  sulphur  that  burns  produces  suffi- 
cient heat  to  melt  the  remainder  of  the  sulphur,   which 
sinks  down  through  the  pile  and  runs  out  of  the  bottom 
into  a  collecting  pooL 

192.  Purification.  —  This  crude  sulphur  is  purified  by 
heating  in  iron  retorts  (Fig.  49)  and  passing  the  vapor- 
ized sulphur  into  brick  chambers,  where  it  deposits  on 
the  cool  wall  as  a  fine  powder,  known  as  flowers  of  sulphur. 


192 


SULPHUR  AND  SULPHIDES 


Soon,  however,  the  walls  become  warm  and  most  of  the 
vaporized  sulphur  condenses  as  a  liquid,  which  makes  its 

way  to  the  outlet  of  the 
condensing  chamber.  It 
is  then  cast  in  wooden 
cylindrical  molds  about 
an  inch  and  a  half  in 
diameter.  This  form 
is  roll  sulphur,  or  brim- 
stone. 

193.   Forms  of  Sulphur. 

—  No  element  displays 
a  greater  variety  of 
forms  than  sulphur. 
Three  of  these  are  well 
known  and  are  easily 
obtained  by  the  follow- 
ing methods : 

(1)  Crystallization 
from  carbon  disulphide. 
Carbon  disulphide.  Dissolves  powdered  roll  sulphur  very 
readily.  The  solvent  evap- 
orates quickly  at  ordinary 
temperatures ;  so  that  as  the 
solution  stands,  the  sulphur 
soon  begins  to  be  deposited, 
just  as  salt  is  deposited  when 
a  solution  of  it  is  evapo- 
rated. The  sulphur  is  de- 
posited in  crystals  of  a  beau- 
tifully regular  octahedral 
shape.  This  form  is  orthorhombic  sulphur  (Fig.  50).  It 
is  soluble  in  carbon  disulphide,- and  has  a  density  of  2.01. 


FIG.  49.—  PURIFICATION  -OF  SULPHUR. 


FIG.  50.  —  RHOMBIC  SULPHUR  CRYS- 
TALS, MAGNIFIED. 


FORMS   OF  SULPHUR 


193 


(2)  Crystallization  of  melted  sulphur. 

Sulphur  is  melted  and  then  allowed  to  cool  until  crys- 
tals appear  at  the  surface ;  on  pouring  off  the  still  liquid 
sulphur,  the  solid  part  is  found  in  crystals  shaped  like 
long,  narrow  prisms  with  sharp  ends  (Fig.  51).  This 
kind  of  sulphur  is  known  as  prismatic  sulphur.  Its  density 
is  1.96,  and  it  differs  in  other  properties  from  the  rhombic 
variety  (page  201).  The  prismatic  form  is  unstable.  On 
standing  a  few  days,  its  crystals  lose  their  transparency, 
become  more  brittle, 
and  increase  in  density. 
Examination  by  polar- 
ized light  shows  that 
the  long,  narrow  prisms 
have  broken  up  into  mi- 
nute rhombic  crystals. 

(3)  Sudden    cooling 
of  boiling  sulphur. 

By  application  of 
considerable  heat  sul- 
phur can  be  made  to 

boil.     Before  it  reaches 

.,     i     .,.  .    ,  SAACO\  FIG.  51.  —  PRISMATIC  SULPHUR. 

its  boiling  point  (445  ) 

it  goes  through  some  interesting  and  unusual  changes. 
When  just  above  its  melting  point,  sulphur  is  a  mobile  liquid 
of  a  light  amber  color.  As  the  temperature  rises,  the  sul- 
phur darkens  rapidly  and  thickens  so  that  it  can  hardly 
be  poured  from  the  inverted  test  tube ;  on  further  heat- 
ing, it  again  becomes  less  viscous,  and  finally  boils,  form- 
ing a  pale  orange  vapor. 

When  boiling  sulphur  is  poured  into  cold  water,  the 
cooled  sulphur  assumes  a  form  (Fig.  52)  quite  different 
in  appearance  from  any  of  those  forms  already  described. 
It  is  without  crystalline  form,  of  a  rubber-like  consistency, 


194 


SULPHUR  AND  SULPHIDES 


and  light  amber  in  color.  Because  of  its  lack  of  crystal- 
line form  it  is  called  amorphous  sulphur.  This  differs 
from  the  rhombic  form  in  being  insoluble  in  carbon  disul- 
phide.  It  is  sometimes  spoken  of  as  plastic  sulphur. 
Like  prismatic  sulphur,  it  is  unstable  and  is  changed  in 

the  course  of  a  few  days  into 
the  stable  rhombic  form. 
In  this  change  the  amor- 
phous sulphur  loses  its 
plastic  character  and  be- 
comes soluble  in  carbon  di- 
sulphide. 

If  sulphur  is  dissolved 
in  some  alkali,  as  sodium 
hydroxide,  and  hydrochloric 
acid  added  to  the  solution, 
a  white,  finely  divided  pre- 

FIG.  52. -AMORPHOUS  SULPHUR.       ^ipitate  is   obtained.       This 

precipitate    is    a    form    of 

amorphous  sulphur.  When  shaken  with  water  it  gives 
a  fluid  known  as  milk  of  sulphur. 

194.  Allotropic  Forms.  —  A   number  of  other  elements 
besides  sulphur  occur  in  several  different  modifications, 
known  as  allotropic  forms.     The  graphite  used   in  lead 
pencils  and  the  diamond  are  two  of  the  allotropic  forms 
of  carbon.     These  two  forms  are  strikingly  different  in 
physical  properties,  but  they  are  the  same  element,  car- 
bon.    Oxygen  and  ozone  are  allotropic  forms.     Allotropic 
forms  are  varieties  of  the  same  element,  differing  in  prop- 
erties on  account  of  varying  energy  content.     They  can  be 
converted  into  one  another. 

195.  Stability  of  the  Allotropic  Forms.  —  At  temperatures 
up  to  96°  C.  all  forms  of  sulphur  tend  to  assume  the  rhom- 


CHEMICAL  PROPERTIES  195 

bic  form.  From  96°  to  114°  the  stable  form  is  the  pris- 
matic variety.  If  crystals  of  the  rhombic  variety  are  put 
into  a  test  tube  and  kept  standing  in  boiling  water  for 
several  days,  the  form  will  be  changed  to  minute  crystals 
of  the  prismatic  variety.  Thus  it  is  seen  that  the  form 
which  the  sulphur  assumes  depends  on  the  temperature. 
It  is  generally  true  that  each  of  the  allotropic  forms  of 
any  element  is  stable  under  certain  definite  conditions. 

Roll  sulphur  consists  entirely  of  the  rhombic  variety. 
Flowers  of  sulphur  are  made  up  of  the  rhombic  form  to- 
gether with  a  smaller  proportion  of  the  amorphous  form, 
as  is  shown  by  the  fact  that  flowers  of  sulphur  are  only 
partly  soluble  in  carbon  disulphide. 

196.  Chemical  Properties.  —  All  forms  of  sulphur  burn 
readily  when  heated  in  the  presence  of  oxygen  ;  sulphur 
dioxide  is  formed  as  a  product  of  the  action.  Sulphur  is 
capable  of  taking  oxygen  away  from  compounds : 

S  +  02— ^S02 

It  does  not,  however,  make 
a  very  satisfactory  reduc- 
ing agent,  because  it  is  apt 
to  combine  with  the  prod- 
ucts of  the  reduction. 

Sulphur  is  a  moderately 
active  element.  It  com- 
bines readily  with  many 
metals,  often  with  the  evo- 
lution of  light  and  heat. 
In  a  sense,  then,  it  may  be  FlG-  53- 

said  to  support  combustion.  This  can  be  shown  by  heat- 
ing sulphur  in  a  test  tube  until  it  boils  and  the  sulphur 
vapor  nearly  fills  the  tube;  on  placing  a  strip  of  very 


196  SULPHUR  AND  SULPHIDES 

thin  copper  in  the  tube,  it  takes  fire  and  burns,  copper 
sulphide  being  formed: 

Cu  +  S  — ^CuS 

Powdered  zinc  and  sulphur,  if  mixed  in  certain  propor- 
tions, will  combine  almost  explosively  when  ignited,  with 
the  formation  of  zinc  sulphide  (Fig.  53) : 

Zn  +  S  — >•  ZnS 

Sulphur  does  not  unite  very  readily  with  non-metals. 
Such  compounds  are,  in  general,  not  very  stable. 

197.  Sulphides.  —  The  metallic  sulphides  form  a  very  im- 
portant class  of  compounds.     Many  metals  are  extracted 
from   sulphide  ores.     Most  of   the    sulphides,    excepting 
those  of  the  extremely  metallic  elements,  are  insoluble  in 
water.     They  usually  have  characteristic  colors. 

The  blackening  or  tarnishing  of  metals  is  sometimes 
due  to  the  action  of  sulphur.  This  is  particularly  true  of 
silver.  Sulphur  or  sulphur  compounds  get  into  the  air 
from  illuminating  gas  or  burning  coal  and,  acting  on  sil- 
ver* produces  the  black  sulphide. 

The  tarnishing  of  silverware  by  the  yolk  of  an  egg  or 
by  mustard  is  due  to  the  sulphur  compounds  contained  in 
these  substances.  Brass  and  copper  are  also  readily  tar- 
nished by  sulphur  and  some  of  its  compounds. 

198.  Resemblances  of  Sulphur  to  Other  Elements.  —  In  the 

ease  with  which  it  combines  with  other  elements,  particu- 
larly metals,  sulphur  resembles  both  chlorine  and  oxygen. 
Generally  it  displays  the  closer  resemblance  to  oxygen. 
This  is  shown  by  comparing  the  solubility  in  water  of 
oxides  and  sulphides.  Those  metals  which  form  insoluble 
oxides  also,  as  a  rule,  form  insoluble  sulphides. 


HYDROGEN  SULPHIDE  197 

In  many  of  its  compounds  sulphur,  like  oxygen,  has  a 
valence  of  two.  Therefore  the  sulphides  and  the  oxides 
of  many  of  the  elements  have  similar  formulas : 

ELEMENT  SULPHIDE  OXIDE 

1  Copper  CuS  CuO 

r  Zinc  ZnS  ZnO 

Hydrogen  H2S  H2O 

^Magnesium  MgS  MgO 

p  Mercury  HgS  HgO 

199.  Uses  of  Sulphur.  —  Sulphur  is  used  in  making  sul- 
phur dioxide,  which  is  employed  for  bleaching  and  disin- 
fecting.    Sulphur  or   some  compound  of   sulphur  serves 
for  the  hardening  (vulcanizing)  of  rubber.     Sulphur  is 
more  or  less  important  for  the  manufacture  of  fireworks 
and  gunpowder,  while  increasing  uses  are  in  the  making 
of   carbon   disulphide   and   the  dyes   known   as    sulphur 
colors.     Sulphur  is  extensively  used  as  a  constituent  of 
sprays  used  on  trees. 

HYDROGEN   SULPHIDE 

200.  Preparation.  —  Hydrogen  sulphide,  H2S,  is  formed 
slowly  and  in  small  quantity  when  hydrogen  is  passed 
over    heated    sulphur 

(Fig.  54).  The  presence 
of  the  gas  is  shown  by 
the  blackening  of  a  strip 
of  paper  (aa)  moistened 
with  lead  acetate.  The 
difficulty  of  forming  hy- 
drogen sulphide  by  the  FIG.  54. 
direct  union  of  the  elements  is  in  strong  contrast  to  the 
great  readiness  with  which  the  hydrogen  compounds,  so 
far  studied,  are  formed.  The  lack  of  a  strong  tendency 


198 


SULPHUR  AND   SULPHIDES 


of   hydrogen   and   sulphur  to  combine  indicates  the  un- 
stable character  of  their  product. 

When  albumen  or  other  organic  matter, 
containing  sulphur,  decays,  hydrogen  sul- 
phide is  one  of  the  substances  formed.  If 
a  little  sulphur  is  added  to  a  fermenting 
sugar  solution,  hydrogen  sulphide  is  pro- 
duced. 

For  practical  use  hydrogen  sulphide  is 
readily  formed  by  the  action  of  dilute  hy- 
drochloric acid  on  ferrous  sulphide  (Fig. 
55): 


FIG.  55. 


FeS  +  2  HC1 


FeC 


H2S 


The  hydrogen  sulphide  passes  off  readily  as  a  gas ;  for 
this  reason  the  double  decomposition  proceeds  rapidly. 
The  sulphides  of  some  other  metals  could  be  used  in  place 
of  the  ferrous  sulphide,  and  instead  of  hydrochloric  acid 
dilute  sulphuric  acid  might  be  used.  The  gas  may  be  col- 
lected by  downward  displacement. 

201.  Physical  Properties.  — Hydrogen  sulphide  is  a  color-  , 
less  gas,  slightly  heavier  than  air,  having  a  characteristic 
odor  resembling  rotten  eggs.     It  dissolves  to  some  extent 
in  water,  and  therefore  is  not  usually  collected  over  this 
liquid.     It  is  generally  collected  by  the  displacement  of 
air.     A  water  solution  of  the  gas  is  sometimes  used  in  the 
laboratory,  but  in  such  a  solution  the  gas  is  decomposed 
in  a  few  days  by  action  with  the  oxygen  of  the  air.     Be- 
sides being  unpleasant,  it  is  injurious  to  inhale  the  gas, 
as  headache  and  sickness  are  apt  to  result. 

202.  Chemical  Properties.  —  The   gas   burns   readily,    if 
there  is  an  ample  supply  of  oxygen,  forming  water  and 


FORMATION  OF  SULPHIDES  199 

sulphur   dioxide  ;    with   a   limited   quantity    of    oxygen, 
sulphur  is  formed  : 

2  H2S  +  3  O2—  ^  2  H2O  +  2  SO2 
2H2S+     02—  *-2H20  +  2S 

On  being  heated  moderately,  hydrogen  sulphide  breaks  up 
into  hydrogen  and  sulphur. 

The  fact  that  a  water  solution  of  hydrogen  sulphide  is 
a  poor  conductor  of  electricity,  shows  that  as  an  acid  it  is 
very  weak.  The  solution  reddens  blue  litmus  very  slowly, 
and  the  color  is  never  as  deep  as  that  produced  by  solu- 
tions of  strong  acids. 

203.  Formation  of  Sulphides.  —  Hydrogen  sulphide  acts 
on  most  metals,  forming  sulphides  and  liberating  hydrogen: 

Pb  +  H2S  —  »-  PbS  +  H2 


2Ag  +  H2S— 

If  hydrogen  sulphide  is  passed  into  a  solution  of  copper 
sulphate,  copper  sulphide  is  formed  : 

CuS04  +  H2S  —  >-  CuS  +  H2S04 

A  similar  reaction  occurs  with  the  dissolved  salts  of  many 
rnetals,  as  lead,  silver,  and  tin.  In  such  cases  the  deter- 
mining factor  that  makes  the  action  possible  is  the  insolu- 
bility of  the  metallic  sulphide  either  in  water  or  in  the 
dilute  acid  that  is  formed  as  a  result  of  the  action.  We 
have  seen  that  metallic  sulphides  can  generally  be  formed 
in  three  different  ways,  for  example  : 

2Ag+      S— 
2Ag+H2S— 
2  AgNO3  +  H2S  —  +-  Ag2S  +  2  HNO3 

The  possibility  of  precipitating  metallic  sulphides  by  this 
third  method  is  of  great  value  to  the  analytical  chemist 


200 


SULPHUR   AND   SULPHIDES 


in  determining  the  composition  of  unknown  substances. 
The  identification  of  the  metal  in  a  particular  case  is  made 
by  means  of  the  color  of  the  sulphide,  its  solubility  in 
various  reagents,  or  other  characteristic  reactions. 

TABLE  OF  SULPHIDES 


NAME 

FORMULA 

COLOR 

DISSOLVES  IN 

Mercuric  sulphide 

HgS 

Black 

Aqua  regia 

Copper  sulphide 

CuS 

Black 

Concentrated  nitric  acid 

Cadmium  sulphide 

CdS 

Yellow 

Concentrated  nitric  acid 

Arsenic  sulphide 

As0S3 

Yellow 

Yellow  ammonium  sulphide 

Antimony  sulphide 

Sb2S8 

.Orange 

Yellow  ammonium  sulphide 

Zinc  sulphide 

ZuS 

White 

Dilute  acids 

204.  Sulphur  Springs.  —  Hydrogen  sulphide  is  produced 
in  nature  in  several  ways.  We  have  mentioned  its 
production  during  the  decay  of  certain  organic  mat- 
ter. Calcium  sulphide  is  formed  when  decaying  matter 
reduces  calcium  sulphate.  Water  reacts  with  calcium 
sulphide,  forming  calcium  hydroxide  and  hydrogen  sul- 
phide ;  the  calcium  hydroxide  is  converted  into  the  car- 
bonate by  the  action  of  water  containing  carbon  dioxide. 


CaS04  -  4  O 
CaS  +  2  H20 


H2C03 


CaS 
H2S 
CaCO 


Ca(OH)2 


2  H2O 


Ca(OH)2 

The  presence  of  hydrogen  sulphide  in  the  waters  of  some 
sulphur  springs  is  accounted  for  by  these  reactions. 


SUMMARY 

Sulphur  is  found  uncombined  (native),  or  combined  in  the  form 
of  sulphides  and  sulphates.     In  Louisiana  it  is  melted  underground 


SUMMARY 


201 


and  forced  to  the  surface.     It  is  extracted  in  Sicily  by  melting  it 
out  from  the  earth  with  which  it  is  mixed. 

Commercial  forms  of  sulphur  are  flowers  of  sulphur  and  lump 

sulphur. 

Allotropic  forms  of  an  element  are  varieties  of  the  same  element 
differing  in  properties. 

Allotropic  forms  of  sulphur  are  the  rhombic,  the  prismatic,  and 
the  amorphous.     The  latter  exists  in  several  modifications. 


RHOMBIC  SULPHUR 

PBISMATIC  SULPHUB 

Specific  gravity 

2.07 

1.96 

Solubility 

Soluble  in  carbon 
disulphide 

Insoluble  in  carbon 
disulphide 

Stability 

Stable  below  96° 

Stable  between  96° 
and  114° 

Sulphur  melts  at  114°  and  boils  at  445° ;  it  is  a  non-conductor 
of  electricity. 

Sulphur  is  a  moderately  active  element,  burns  in  air,  and  unites 
directly  with  many  elements. 

Sulphur  is  used  for  making  sulphur  dioxide,  sulphur  acids,  sul- 
phides, and  carbon  disulphide.  Rubber  is  vulcanized  by  sulphur  or 
some  of  its  compounds. 

Hydrogen  sulphide  occurs  in  volcanic  gases  and  in  water  of  sul- 
phur springs,  and  is  formed  in  nature  by  decay  of  organic  matter 
containing  sulphur. 

Hydrogen  sulphide  is  prepared  by  the  action  of  hydrochloric  acid 
or  of  sulphuric  acid  with  ferrous  sulphide. 

It  is  a  colorless  gas,  poisonous,  and  possessing  a  characteristic, 
disgusting  odor.  One  volume  of  water  at  20°  dissolves  3. 1  volumes 
of  hydrogen  sulphide. 


202  SULPHUR  AND  SULPHIDES 

The  water  solution  is  a  weak  acid  and  forms  sulphides  with  most 
metallic  ions. 

The  gas  burns  in  a  limited  supply  of  air  to  form  water  and  sul- 
phur, and  in  an  excess  of  air  forms  water  and  sulphur  dioxide. 

Hydrogen  sulphide  is  used  by  chemists  to  precipitate  certain 
metals  from  solutions  as  sulphides. 


EXERCISES 

1.  Compare,  as  to  efficiency,  the  Sicilian  with  the  Louisiana 
process  for  the  extraction  of  sulphur.  ft  u.^ 

2.  Describe  the  process  that  a  piece  of  native  sulphur  un- 
dergoes before  it  is  placed  on  the  market  as  flowers  of  sulphur. 

3.  Explain  (in  the  Louisana  process  for  obtaining  sulphur) 
the  uses  of  (a-)  the  hot  water,  (6)  the  hot,  compressed  air,  (c)  the 
wooden  bins. 

4.  What  is  meant  by  the  allotropic  forms  of  an  element? 
Name  the  allotropic  forms  of  sulphur,.,  ^ 

a/h  '-r  1  •'-'  ^"       '  ^  ''' '*•*(-{_  1^     $  CJ- L. '.  Y-W*  •      •  /'  '    '  '  -'w  •  '          1  ! 

5.  State  what  allotropic  forms  of  sulphur  exist  in  each  of 
the  following  commercial  varieties :   roll  sulphur,  milk  of  sul- , 
phur,  and  flowers  of  sulphur.     /  *• 

6.  What  conditions  determine  whether  sulphur  is  to  assume 
the  prismatic  or  the  rhombic  form  ?    & 

7.  How  would  you  prepare  milk  of  sulphur  from  a  piece  of 
roll  sulphur  ?  Q^yu^^r/trt-  Mf  A/**  A7 ..  j 

8.  Why  is  a  sulphur  candle,. sometimes  used  for  fumigation? 

y/x.    ^  3.^-    4'y^  fy".:'-f<j      4Fl£.    -•_.       '  '-f~l<4,'-'~t '•'  ?*"£•*-<.• 

9.  Why  does  silverware  tarnish  so  readily  in  large  cities  ? 

10.  Write  the  formulas  of  five  sulphides  and  the  formulas 
of  the  corresponding  oxides. 

11.  Starting  with  iron,  sulphur,  and  hydrochloric  acid,  give 
directions  for  the  preparation  of  hydrogen  sulphide. 

12.  How  many  grams  of  ferrous  sulphide  would  be  required 
for  the  preparation  of  five  liters  of  hydrogen  sulphide  ? 


EXERCISES  203 

13.  Account  for  the  particles  of  sulphur  found  in  a  bottle  in 
which  a  water  solution  of  hydrogen  sulphide  has  been  standing 
for  some  days.     How  would  the  contents  smell  ?     Write  the 
equation  for  the  reaction  that  has  taken  place. 

14.  Under  what  conditions  is  sulphur  deposited  when  hydro- 
gen sulphide  burns  ? 

15.  How  many  liters  of  oxygen  would  be  required  for  the 
complete  combustion  of  four  liters  of  hydrogen  sulphide  ? 

16.  Account  for  the  fact  that  a  water  solution  of  hydrogen 
sulphide  is  not  so  active  an  acid  as  a  water  solution  of  hydro- 
gen chloride. 

17.  How  many  grams  of  hydrogen  sulphide  would  be  re- 
quired to  combine  with  the  copper  in  0.1  gram  of  copper  sul- 
phate ? 

18.  Account  for  the  unpleasant  taste  of  the  waters  of  sul- 
phur springs. 

19.  Calculate  the  weight  of  a  liter  of  hydrogen  sulphide 
measured  under  standard  conditions. 

20.  How  could  hydrogen  sulphide  be  used  to  distinguish  the 
solution  of  a  zinc  salt  from  a  solution  of  a  copper  salt  ? 

C  v/x  0 

0      ,  ^^  ^ 

dvu  0 


V 


->  14  S  + 

, 


CHAPTER   XX 

OXIDES  AND  ACIDS  OF  SULPHUR 
SULPHUR   DIOXIDE 

205.  Preparation  by  Direct  Combination —  When  sulphur 
burns  in  oxygen  or  in  air,  sulphur  dioxide  is  formed : 

S  +  O2 — ^SO2 

The  odor  of  burning  sulphur  is  due  to  the  dioxide  formed. 
Many  ores  are  sulphides  of  metals,  and  large  quantities  of 
sulphur  dioxide  are  prepared  by  roasting  such  ores  in  air. 


FIG.  56.  —  PREPARATION  OF  SULPHUR  DIOXIDE. 
a,  generator ;  b,  safety  bottle. 

206.  Preparation  by  Reduction  of  Sulphuric  Acid.  —  When 
copper,  silver,  or  mercury  is  treated  with  hot,  concentrated 
sulphuric  acid,  sulphur  dioxide  is  formed  (Fig.  56). 
The  chemical  action  is  complicated,  but  it  is  probable  that 

204 


PREPARATION  OF  SULPHUR  DIOXIDE          205 

the  acid  first  acts  with  the  metal,  and  hydrogen  is  dis- 
placed, according  to  the  equation  : 

Cu  +  H2SO4  — >-  CuSO4  +  2  H 

The  hydrogen  is  then  oxidized  to  water  by  the  excess  of 
hot,  concentrated  sulphuric  acid.  This  oxidation  is  ac- 
complished at  the  expense  of  the  reduction  of  the  sulphu- 
ric acid  to  sulphurous  acid,  according  to  the  equation  : 

H2SO4  +  2  H  — >-  H2SO3  +  H2O 

The  sulphurous  acid  decomposes,  as  soon  as  it  is  formed, 
into  water  and  sulphur  dioxide,  according  to  the  equation  : 

H2S08— ^H20  +  S02 

The  changes  indicated  in  the  three  equations  given  above 
go  on  together.  The  total  change  may  be  represented  by 
the  one  equation  : 

Cu  H-  2  H2SO4 — >•  CuSO4  +  2  H2O  +  SO2 

Some  copper  sulphide  is  formed  by  the  reaction  of 
copper  with  hot,  concentrated  sulphuric  acid. 

207.  Preparation  by  Decomposition  of  a  Sulphite.  —  When 
a  mixture  of  sodium  sulphite  and  dilute  sulphuric  acid  is 
gently  heated  in  a  flask,  sulphur  dioxide  is  evolved,  ac- 
cording to  the  equation  : 

Na2SO3  +  H2SO4  — >-  Na2SO4  +  H2O  +  SO2 

Possibly  sulphurous  acid  is  first  formed,  but  if  so,  this 
unstable  compound  immediately  decomposes  into  water 
and  sulphur  dioxide.  The  equations  are  : 

XT~  °^    f  H2S04-^Na2S04  +  H2S08 

Ho/-\  TT  n  -  ori 

20<J3  *-  ±12U    +   fcUn 


206 


OXIDES  AND  ACWS  OF  SULPHUR 


The  evolution  of  the  gas  may  be  made  very  regular  by 
using  sodium  acid  sulphite  and  allowing  sulphuric  acid 

(1  to  1)  to  fall  on  it,  drop  by 

drop  (Fig.  57). 


208.  Physical    Properties. 

—  Pure  sulphur  dioxide  is  a 
colorless  gas,  with  a  suffocating 
odor,  and  is  more  than  twice 
as  heavy  as  air.  It  is  very 
soluble  in  water  ;  one  volume 
of  water  dissolves  many  times 
its  own  volume  of  the  gas  at 
ordinary  temperatures.  The 
gas  may  be  completely  expelled 
from  the  solution  by  boiling. 


FIG.  57. 


Sulphur  dioxide  is  one  of  the 
easiest  gases  to  liquefy.  At 
ordinary  temperatures,  a  pres- 
sure of  but  two  atmospheres 
is  required ;  at  the  tempera- 
ture of  a  freezing  mixture  of 
ice  and  salt,  the  ordinary  at- 
mospheric pressure  is  sufficient 
to  change  the  gas  to  a  liquid. 
Liquid  sulphur  dioxide  is  sold 
in  glass  or  metal  siphons  (Fig. 
58). 

209.  Chemical  Properties. — 

The  solution  of  sulphur  dioxide 
has  an  acid  reaction  and  neu- 
tralizes bases,  forming  sul- 
phites. Thus  with  sodium  hy- 


FIG.  58. 


ANHYDRIDES  207 

droxide  the  reaction  results  in  the  formation  of  sodium 
sulphite  and  water.  This  indicates  the  presence  in  the 
solution  of  hydrogen  and  sulphite  ions,  or,  in  other  words, 
the  solution  contains  sulphurous  acid.  This  acid,  how- 
ever, has  never  been  separated  from  the  solution.  The 
acid  is  formed  according  to  the  equation  : 

H2O  +  SO2  — -^H2SO8 

If  a  solution  of  sulphurous  acid  is  allowed  to  stand  in 
contact  with  air,  it  gradually  takes  up  oxygen,  forming 
sulphuric  acid,  according  to  the  equation  : 

2H2S03  +  02  — ^2H2S04 

Sulphites  are  likewise  changed  to  sulphates. 

210.  Anhydrides.  —  Many  oxides  unite  with  one  or  more 
molecules  of  water  to  form  new  compounds.     Such  oxides 
are  called  anhydrides  (meaning  "  without  water ").     An 
anhydride  is  an  oxide  which  unites  with  water  to  form  an 
acid  or  a  base.     Anhydrides  are  classified  as  acid  or  basic, 
according  to  whether  they  form  acids  or  bases  in  "combin- 
ing with  water.     Calcium  oxide,  CaO,  is  a  basic  anhydride, 
as  shown  by  the  equation  : 

CaO  +  H2O  — »-  Ca(OH)2 

Slaked  lime,  Ca(OH)2,  is  a  base.  Since  sulphur  dioxide 
unites  with  water  to  form  an  acid,  it  is  called  an  acid  anhy- 
dride. An  acid  anhydride  is  named  from  the  acid  it  forms 
when  it  unites  with  water.  Hence  sulphur  dioxide  is 
called  sulphurous  anhydride. 

211.  Reducing  Action  of  Sulphur  Dioxide.  — Since  sulphu- 
rous acid  is  so  readily  oxidized,  it  acts  as  a  reducing  agent 
in  many  cases.     Potassium  permanganate  is  reduced  by 


208 


OXIDES  AND  ACIDS   OF  SULPHUR 


sulphurous  acid   to   potassium    sulphate    and  manganese 
sulphate  : 


2  KMnO 


5  H2SO3 


K2SO4  +  2  MnSO4 


-h2H2S04+3H20 

In  a  similar  way  chromic  acid  may  be  reduced  to  chro- 
mium sulphate.  This  reducing  action,  in  the  presence  of 
water,  probably  explains  the  bleaching  action  of  sulphur 
dioxide  in  some  cases.  The  coloring  matter  is  reduced, 
thus  decolorizing  the  substance.  In  other  cases,  the  sul- 
phur dioxide  unites  directly  with  the  coloring  matter, 
producing  a  colorless  compound.  The  color  of  materials 
bleached  by  sulphur  dioxide  will  often  return  on  expo- 
sure to  the  air,  as  in  the  case  of  straw.  Bleaching  by 
chlorine  is  more  permanent. 

212.    Uses.  —  Great  quantities  of  sulphur  dioxide  or  of 
sulphites  are  used  in  the  bleaching  of  many  organic  color- 

ing matters.  Straw,  silk, 
wool,  and  other  materials, 
which  would  be  injured  by 
chlorine,  are  decolorized 
by  sulphur  dioxide  (Fig. 
59).  Cherries  are  some- 
times bleached  with  sul- 
phurous acid  and  then 
colored  with  the  bright 
shades  that  are  seen  in 
the  canned  goods  of  com- 

merce' 

Sulphur  dioxide  is  some- 

times used  as  a  disinfectant. 

For  this  purpose,  sulphur  is  burned,  or  liquid  sulphur 
dioxide  is  allowed  to  evaporate  in  the  room  to  be  disin- 


FIG.  59.  —  A   CARNATION   IN  AIR  (a) 
AND  IN  SULPHUR  DIOXIDE  (&). 


USES  OF  SULPHUR  DIOXIDE  209 

fected.  In  either  case,  the  room  should  be  tightly  closed 
and  the  air  in  the  room  be  kept  moist,  so  that  the  disease 
germs  may  be  killed  by  the  sulphurous  acid  formed.  This 
power  of  sulphurous  acid  to  kill  lower  organisms  is  the 
reason  for  its  use  in  the  curing  of  wine  and  beer.  The 
growth  of  mold  is  thus  prevented.  An  increasing  but 
questionable  use  of  the  acid  is  its  employment  as  a  food 
preservative.  Sulphur  dioxide  not  only  attacks  lower  or- 
ganisms, but  is  decidedly  injurious  to  higher  forms  of 
life.  Vegetable  growth  is  blighted  in  the  neighborhood 
of  smelters  and  chemical  works  where  the  gas  is  generated. 
In  cities,  the  gases  from  the  burning  of  coal  containing 
sulphur  have  a  like  effect. 

The  most  important  use  of  sulphur  dioxide,  however,  is 
in  the  manufacture  of  sulphuric  acid.  Immense  quantities 
are  used  for  this  purpose. 

SULPHUR   TRIOXIDE 

213.  Preparation.  —  Sulphur  trioxide  is  prepared  by  the 
oxidation  of  sulphur  dioxide.  It  is  formed  in  small  quan- 
tities when  sulphur  burns,  and  its  presence  causes  the 
cloudiness  often  observed  in  sulphur  dioxide.  This  oxida- 
tion may  be  made  more  rapid  by  the  presence  of  catalytic 
agents.  Finely  divided  platinum  and  ferric  oxide  are  the 
more  important  ones.  Platinized  asbestos  is  prepared  by 
soaking  asbestos  in  platinum  chloride  and  heating  until 
finely  divided  platinum  is  left  on  the  asbestos.  A  mixture 
of  sulphur  dioxide  and  air  is  passed  over  platinized  asbes- 
tos (Fig.  60)  and  sulphur  trioxide  is  formed.  The  tem- 
perature must  be  carefully  regulated,  as  the  trioxide 
decomposes  at  a  temperature  only  a  little  higher  than  that 
necessary  for  its  formation.  The  reaction  is  then  reversi- 
ble and  may  be  represented : 


210 


OXIDES  AND  ACIDS   OF  SULPHUR 


214.  Solubility.  —  Sulphur    trioxide    (sulphuric    anhy 
dride)  dissolves  in  water,  forming  sulphuric  acid : 

S08+H20— *-H2S04 

As  produced  by  the  contact  process,  however,  sulphur  tri- 
oxide is  not  readily  soluble  in  water.  It  is  much  more 
soluble  in  concentrated  sulphuric  acid,  with  which  it 
forms  a  complex  compound,  called  fuming  sulphuric  acid, 
H2S04.S03. 

H2S04  +  S03  —>-  H2S04  •  S03 

SULPHURIC   ACID 

215.  Preparation  by  Contact  Process.  —  The  experimental 
preparation  of  sulphur  trioxide  and  sulphuric  acid  by  the 


"To  Aspirator 


FIG.   60. — LABORATORY  PREPARATION  OF  SULPHUR  TRIOXIDE. 

contact  method  is  represented  in  Fig.  60.  Sulphur 
(a)  burns  in  the  air  drawn  into  the  apparatus  by  an 
aspirator,  and  the  sulphur  dioxide  formed  passes  with  the 
excess  of  air  into  the  U-tube  £  which  is  filled  with  some 


PREPARATION  BY  CONTACT  PROCESS 


211 


loose  material  to  rid  the  gases  of  sulphur  dust.  In  the 
bottle  (<?)  the  gases  lose  their  moisture  as  they  make  their 
way  through  the  glass  beads  drenched  with  concentrated 
sulphuric  acid.  The  platinized  asbestos  in  the  tube  (c?)  is 
gently  heated,  and  brings  about  the  union  of  the  sulphur 
dioxide  with  the  oxygen  of  the  air.  The  sulphur  tri- 
oxide  resulting  from  the  action  is  absorbed  by  concentrated 
sulphuric  acid  trickling  down  through  the  apparatus  (e). 
Water  may  be  used  for  this  last  absorption,  but  is  not 
nearly  so  efficient. 


7) 


FIG.  61.  —  CONTACT  PROCESS  (DIAGRAMMATIC). 

A,  blower;  B,  pyrites  burner;  C,  dry  scrubber  filled  with  coke;  D,  wet 
scrubber  filled  with  coke  wet  with  sulphuric  acid ;  £,  arsenic  purifier  ; 
F,  heater;  G,  contact  chamber;  H,  absorber  (concentrated  sulphuric 

acid). 

Pure  concentrated  sulphuric  acid  is  prepared  commer- 
cially from  sulphur  trioxide  made  by  the  method  just 
stated.  Sulphur,  or  ores  containing  sulphur,  is  burned 
in  a  furnace  with  air  (Fig.  61,  B).  The  sulphur  dioxide 
and  the  other  gaseous  products  of  combustion  are  cooled, 
and  freed  from  dust  ((7,  D),  arsenic  (^7),  and  most  of  the 


212  OXIDES  AND  ACIDS   OF  SULPHUR 

moisture ;  the  purified  gases  are  then  mixed  with  air 
and  passed  through  a  tube  (6r)  containing  a  catalytic 
agent,  usually  finely  divided  platinum.  Unless  the  im- 
purities are  removed,  they  act  on  the  platinum  and  it 
soon  loses  its  catalytic  power.  The  oxygen  of  the  air 
combines  with  the  sulphur  dioxide  and  forms  the  trioxide  : 

2S02  +  02— ^2S03 

The  sulphur  trioxide  is  passed  into  concentrated  sulphuric 
acid,  and  the  solution  is  then  diluted : 

H2S04  +  S03  — >-  H2S04  •  S03 
H2SO4  •  S03  +  H20  — »-  2  H2S04 

216.  Preparation  by  Chamber  Process.  —  For  more  than  a 
century,  all  of  the  sulphuric  acid  used  for  commercial  pur- 
poses was  made  by  the  chamber  process.  To-day,  owing 
to  patents  on  the  most  approved  forms  of  apparatus  for 
carrying  on  the  contact  process,  and  to  the  fact  that  man- 
ufacturers dislike  to  abandon  expensive  equipment  in  good 
working  order,  the  chamber  process  is  still  very  extensively 
used  for  the  manufacture  of  commercial  oil  of  vitriol.  The 
commercial  acid  produced  by  this  process  is  not  pure  and 
is  not  concentrated.  It  contains  only  about  60  %  to  70  % 
of  sulphuric  acid.  The  advantage  of  the  contact  process 
over  the  chamber  process  is  that  the  former  directly  pro- 
duces a  pure,  concentrated  acid. 

The  sulphur  dioxide  used  in  the  manufacture  of  sul- 
phuric acid  is  often  obtained  by  heating  in  contact  with  air 
some  sulphide  of  a  metal,  usually  iron  sulphide,  FeS2, 
(pyrites).  The  sulphur  dioxide  is  converted  into  the 
higher  oxide  by  making  use  of  nitrogen  peroxide.  The 
peroxide  is  obtained  by  the  action  of  air  with  nitric  oxide  : 


PREPARATION  BY  CHAMBER  PROCESS         213 

The  nitric  oxide  results  from  the  reaction  of  nitric  acid 
with  water  and  sulphur  dioxide.  The  nitric  acid  is  made 
by  the  action  of  sulphuric  acid  with  sodium  nitrate  in 
vessels  called  niter  pots  : 

2  NaN03  +  H2S04— ^Na2S04  +  2  HNO3 

2  HN08  +  3  S02  +  2  H20— -^3  H2SO4  +  2  NO 

Sulphur  dioxide  mixed  with  nitrogen  peroxide  is  passed 
through  a  tower  called  the  Glover  tower  (Fig.  62),  to 
be  described  later,  and  then  into  large  lead  chambers. 
Within  the  chambers  sulphur  dioxide,  nitric  oxide,  air, 
and  steam  are  brought  together.  Complicated  reactions 
take  place  which  are  not  well  understood. 

Since  approximately  four  fifths  of  the  air  is  nitrogen,  it 
is  necessary  to  provide  for  the  escape  of  the  nitrogen  and 
at  the  same  time  prevent  the  escape  of  the  oxides  of  nitro- 
gen as  far  as  possible.  This  is  accomplished  by  causing 
the  chamber  gases  to  pass  through  the  Gay-Lussac  tower. 
The  tower  is  filled  with  coke.  Concentrated  sulphuric 
acid  (78  %  H2SO4)  is  conveyed  to  the  top  of  the  tower 
and  sprinkled  on  the  coke.  The  chamber  gases- enter  the 
tower  at  the  bottom  and  ascend  against  the  stream  of  sul- 
phuric acid  as  it  trickles  down.  When  the  plant  is  run- 
ning properly,  practically  all  of  the  oxides  of  nitrogen  are 
dissolved  in  the  sulphuric  acid.  In  this  manner  they  are 
caught  in  the  Gay-Lussac  tower,  while  the  nitrogen, 
being  insoluble  in  the  acid,  escapes. 

From  the  bottom  of  the  Gay-Lussac  tower,  the  sulphuric 
acid,  carrying  in  solution  the  oxides  of  nitrogen,  is  pumped 
to  a  tank  on  the  top  of  another  tower,  called  the  Glover 
tower,  situated  between  the  ore  roasters  and  the  chambers. 
.The  Glover  tower  is  similar  in  construction  to  the  Gay- 
Lussac  tower.  It  is  filled  with  lumps  of  quartz.  At  the 


214 


OXIDES  AND  ACIDS   OF   SULPHUR 


PROPERTIES  OF  SULPHURIC  ACID  215 

top  of  the  tower  are  two  tanks,  one  containing  the  liquid 
coming  from  the  Gay-Lussac  tower,  and  the  other  the 
chamber  acid  (55%  H2SO4).  As  a  mixture  of  these  two 
liquids  passes  down  through  the  Glover  tower,  it  meets 
the  hot  gases  coming  from  the  ore  roasters  and  from  the 
nitric  acid  plant,  on  their  way  to  the  lead  chambers.  The 
result  is  that  the  dilute  chamber  acid  is  made  more  con- 
centrated, the  Gay-Lussac  acid  is  decomposed  by  the  water 
in  the  chamber  acid,  and  the  gases  are  allowed  to  enter 
the  chambers,  while  sulphuric  acid  (67  %)  is  obtained  from 
the  bottom  of  the  tower.  This  chamber  acid  can  be  con- 
centrated by  boiling  in  iron  and  then  in  platinum  pans,  but 
for  many  commercial  purposes  needs  no  further  treatment. 

217.  Physical  Properties.  —  Sulphuric   acid  is  a  heavy, 
oily  liquid.     Ordinary  commercial  sulphuric  acid,  called 
oil  of  vitriol,  is  nearly  twice  as  heavy  as  water.     It  boils 
at  a  higher  temperature  (338°)  than  most  of  the  common 
acids,  and  many  of  its  uses  depend  on  this  fact. 

CHEMICAL  PROPERTIES 

218.  Action  with  Water.  —  Sulphuric  acid   mixes  with 
water  in  all  proportions  ;  during  the  mixing  considerable 
heat  is  evolved.     If  such  a  mixture  is  made,  the  acid  should 
be  slowly  poured  into  the  water,  with  constant  stirring.     By 
doing  this,  the  heat  generated  is  distributed  throughout 
the  large  mass  of  water,  and  the  sudden  generation  of 
steam,  which  would  cause  spattering,  is  avoided.     It  is 
not  advisable  to  use  a  glass  vessel  for  mixing  sulphuric 
acid  and  water. 

219.  Dehydrating  Action.  —  Concentrated  sulphuric  acid 
absorbs  moisture  from  the  air,  and  this  tendency  of  the 
acid  to  take  up  water  explains  many  of  its  actions.     Wood, 


216  OXIDES  AND  ACIDS   OF  SULPHUR 

paper,  sugar,  and  similar  substances,  containing  hydrogen 
and  oxygen,  are  charred  by  sulphuric  acid.  The  acid  re- 
moves the  hydrogen  and  oxygen  as  water,  leaving  a  resi- 
due consisting  largely  of  carbon.  On  the  flesh  it  acts 
similarly,  and  a  painful  wound  results. 

.  220.  Action  with  Metals.  —  With  metals  the  acid  acts  in 
two  ways.  If  the  action  takes  place  at  a  low  tempera- 
ture, hydrogen  may  be  evolved,  provided  sufficient  water 
is  present  to  dissolve  the  metallic  sulphate  formed : 

Zn  +  H2S04  — >-  ZnS04  +  H2 
Fe  +  H2SO4  — >•  FeSO4  +  H2 

Mercury,  silver,  and  copper  are  not  acted  on  by  the  cold 
acid,  but  if  concentrated  acid  is  used  and  the  temperature 
raised  sufficiently,  these  metals  react,  reducing  part  of  the 
sulphuric  acid,  forming  sulphur  dioxide,  water,  and  metal- 
lic sulphates  (§  206)  : 

Cu  +  2  H2S04  — ^  CuS04  +  S02  +  2  H2O 

Thus  at  ordinary  temperatures  dilute  sulphuric  acid  may 
act  like  hydrochloric  acid,  exchanging  its  hydrogen  for 
metals,  but  when  hot  and  concentrated,  it  acts  as  an  oxidizing 
agent. 

221.  Action  with  Bases.  —  With  bases  and  metallic  oxides 
it  reacts,  forming  water  and  sulphates  : 

2  KOH  +  H2S04— ^2  H20  +  K2SO4 
Ca(OH)2  +  H2S04— >-2  H2O  +  CaSO4 

ZnO  +  H2S04— >-H20  +  ZnSO4 
Fe2O3  +  3  H2SO4— ^3  H2O  +  Fe2(SO4)3 

222.  Test  for  a  Sulphate.  —  The  sulphates  are  all  soluble 
except  four,  the  sulphates  of  barium,  strontium,  calcium, 


USES  OF  SULPHURIC  ACID  217 

and  lead.  In  detecting  the  SO4  —  ion,  a  solution  of  barium 
chloride  is  usually  employed.  Representing  by  M++  any 
ion  carrying  two  positive  charges  : 

M++SO4—  +  Bz++(C\-\—  >-  BaSO4  +  M 


The  barium  sulphate  is  easily  identified,  because  it  is 
white  and  insoluble  in  water,  dilute  acids,  and  alkalies. 
If,  therefore,  on  adding  barium  chloride,  a  white  precipi- 
tate, which  is  insoluble  in  hydrochloric  acid,  is  obtained, 
the  presence  of  sulphate  ions  is  indicated. 

223.  Uses  of  Sulphuric  Acid.  —  The  absorption  of  water 
by  sulphuric  acid  renders  it  a  good  dehydrating  agent, 
and  in  the  laboratory,  gases  are  dried  by  being  made  to 
bubble  through  it  (Fig.  22).  In  the  manufacture  of  sul- 
phuric acid,  the  air  and  sulphur  dioxide  employed  are 
dried  by  contact  with  sulphuric  acid.  In  the  purification 
of  petroleum  products,  kerosene,  etc.,  it  is  used  to  remove, 
by  charring,  materials  that  would  give  offensive  odors  in 
burning.  In  the  preparation  of  nitroglycerine,  it  aids  the 
reaction  by  absorbing  water. 

As  sulphuric  acid  has  a  higher  boiling  point  than  many 
acids,  it  is  used  in  their  preparation.  Examples  of  this 
action  have  already  been  studied  (§§  82,  200). 

On  account  of  the  conductivity  of  its  solutions,  sul- 
phuric acid  is  used  in  electric  batteries  and  in  plating.  It 
is  used  also  as  a  catalytic  agent  in  the  production  of 
glucose  from  starch  and  water. 

It  is  used  to  dissolve  the  surface  deposit  on  metals, 
previous  to  tinning  or  galvanizing.  This  process  is  called 
"  pickling,"  and  is  essential  if  a  firmly  adherent  coating  is 
to  be  secured.  A  very  important  use  is  the  conversion  of 
certain  insoluble  phosphate  rocks  into  soluble  calcium 
phosphates,  for  use  as  fertilizers.  Enormous  quantities 


218  OXIDES  AND  ACIDS   OF  SULPHUR 

of  it  are  used  in  these  operations,  and  in  hundreds  of 
others.  There  are  few  materials  in  common  use  by  civilized 
man  with  which  sulphuric  acid  has  not  been  directly  or  in- 
directly connected. 

SUMMARY 

Sulphur  dioxide  can  be  prepared  in  several  ways :  direct  com- 
bination of  oxygen  with  free  sulphur  or  with  sulphur  in  sulphides  ; 
reduction  of  sulphuric  acid  ;  decomposition  of  sulphites  with  acids. 

The  characteristic  odor,  the  weight,  and  the  solubility  in  water 
of  sulphur  dioxide  are  three  striking  physical  properties.  Chem- 
ically it  is  an  acid  anhydride,  forming  sulphurous  acid,  which  is  a 
powerful  reducing  agent. 

Sulphur  dioxide  is  used  in  bleaching,  as  a  disinfectant,  as  a 
food  preservative,  and,  most  important  of  all,  in  the  manufacture 
of  sulphuric  acid. 

An  anhydride  is  an  oxide  that  unites  with  water  to  form  an 
acid  or  a  base.  An  acid  anhydride  is  named  from  the  acid  that 
it  forms  with  water. 

Sulphur  trioxide  is  prepared  by  the  oxidation  of  sulphur  dioxide 
by  means  of  a  catalytic  agent. 

Sulphur  trioxide  is  the  anhydride  of  sulphuric  acid.  It  combines 
energetically  with  water. 

Sulphuric  acid  maybe  manufactured  by  the  "  contact  process," 
consisting  of  the  following  steps  : 

(1)  oxidation  of  sulphur  to  the  dioxide  ; 

(2)  catalytic  oxidation  of  the  sulphur  dioxide  to  the  trioxide ; 

(3)  dissolving  the  trioxide  in  concentrated  sulphuric  add  , 

(4)  dilution  of  the  trioxide  solution. 

Sulphuric  acid  is  a  heavy,  oily  liquid  of  high  boiling  point. 

With  metals  sulphuric  acid  acts  in  two  ways.  At  low  tempera- 
tures and  when  dilute,  hydrogen  may  be  evolved  and  the  sulphate 

• 


EXERCISES  219 

of  the  metal  formed.  When  hot  and  concentrated,  it  reacts  with 
certain  metals  as  an  oxidizing  agent,  forming  sulphur  dioxide, 
water,  and  metallic  sulphates.  Sulphuric  acid  acts  with  bases  and 
metallic  oxides  as  a  typical  acid,  forming  water  and  a  sulphate. 

Sulphuric  acid  is  used  as  a  dehydrating  agent ;  in  the  prepara- 
tion of  other  acids  ;  and  in  a  wide  range  of  industrial  applications. 

All  common  sulphates  are  soluble  in  water,  except  those  of  lead, 
barium,  strontium,  and  calcium.  To  test  for  a  sulphate,  add  a 
solution  of  barium  chloride  ;  a  white,  granular  precipitate,  insolu- 
ble in  dilute  hydrochloric  acid,  indicates  the  presence  of  sulphate 
ions. 

EXERCISES 

1.  Which   of   the   laboratory   methods   would  you  use  for 
preparing  pure  sulphur  dioxide  ?     Why  ? 

2.  How  many  liters  (standard  conditions)  of  sulphur  diox- 
ide would  result  from  the  reaction  of  12  grams  of  copper  with 
concentrated  sulphuric  acid  ? 

3.  What  weight  of  sodium  sulphite  must  be  decomposed  to 
furnish  3.5  liters  sulphur  dioxide  (standard  conditions)  ? 

4.  What  advantages  has  sulphur  dioxide  over  chlorine  as  a 
bleaching  agent  ?     What  disadvantage  ? 

5.  Compare  the  chemical  actions  in  chlorine  and  sulphur 
dioxide  bleaching. 

6.  What  is  an  acid    anhydride  ?     Name  two  anhydrides 
containing  sulphur,  and  give  their  formulas. 

7.  Describe  the  manufacture  of  sulphuric  acid  by  the  con- 
tact process. 

8.  How  many  pounds  of  sulphuric  acid  could  be  manufac- 
tured from  120  pounds  of  pure  sulphur  ? 

9.  If  a  bottle  partly  filled  with  concentrated  sulphuric  acid 
is  left  open  to  the  air,  the  liquid  contents  increase.     Explain. 


220  OXIDES  AND  ACIDS   OF  SULPHUR 

10.  Calculate  how  many  grams  (a)  of  silver  sulphate  and 
(b)  of  copper  sulphate  you  could  make  from  a  dime  which  is 
10  %  copper.     A  dime  weighs  2.48  grams. 

11.  Explain  why  concentrated  sulphuric  acid  must  be  poured 
slowly  into  water  when  the  two  liquids  are  mixed. 

12.  Account  for  the  darkened  rings  formed  on  wood  where 
bottles  of  concentrated  sulphuric  acid  have  been  standing. 

13.  Why  can  either  hydrochloric  or  sulphuric  acid  be  used  in 
the  preparation  of  hydrogen  sulphide  ?     Which  of  these  two 
acids  must  be  taken  for  the  preparation  of  nitric  acid.     Why  ? 

14.  Explain  why  boiling   concentrated   sulphuric  acid  pro- 
duces such  frightful  burns. 

15.  Show  how  hot,  concentrated  sulphuric  acid  acts  as  an 
oxidizing  agent  with  metallic  silver. 

16.  What  effect  would  you  expect  if  a  strip  of  lead  were 
placed  in  dilute  sulphuric  acid  ?     Explain. 

17.  Why  is  a  dish  containing  sulphuric  acid  put  inside  the 
case  of  a  delicate  balance  ?     Why  are  clocks  for  keeping  exact 
time  similarly  treated  ? 

18.  Why  is  the  civilization  of  a  country  said  to  be  indicated 
by  the  amount  of  sulphuric  acid  it  uses  ? 

19.  What  is  oil  of  vitriol?     A  dehydrating  agent?     Pick- 
ling a  metal  ? 

20.  What  chemical  tests  would  you  make  to  prove  a  given 
solution  contained  a  sulphate  of  sodium? 


CHAPTER   XXI 
NITROGEN  AND  THE  ATMOSPHERE 

224.  Occurrence.  —  Nitrogen  has  already  been  mentioned 
as  constituting  a  large  portion  of  the  atmosphere.     It  is 
found  in  a  few  mineral  compounds,  most  of  which,  how- 
ever, are  the  result  of  the  activity  of  animal  and  vegetable 
organisms.     Nitrogenous  organic  compounds  exist  in  great 
variety ;  and  one  class,  the  proteins,  of  which  the  white 
of  egg  is  an  example,  are  directly  concerned  with  the  life 
processes.     In  fact,  nitrogen  is  perhaps  the  most  charac- 
teristic element  in  living  organisms,  since  protein  makes 
up  the  living  matter  of  the  muscles  and  the  protoplasm  of 
the  cells.     Life  without  nitrogen  would  be  impossible. 

225.  Preparation.  —  Nitrogen  may  be  prepared  from  air 
by  causing  the  oxygen  to  combine  with  phosphorus  in  the 
presence  of  water.     Phosphorus  is  employed  because  its 
great  tendency  to  combine  with  oxygen  insures  the  com- 
pleteness of  the  reaction,  even  at  ordinary  temperatures, 
and  because  its  oxides  have  a  great  tendency  to  combine 
with  water  and  so  are  rapidly  removed  from  the  gas. 

Other  reducing  agents  may  be  used,  provided  the  oxide 
formed  is  easily  separated  from  the  nitrogen.  If  air  is 
passed  through  a  strongly  heated  tube  containing  reduced 
copper  or  fine-meshed  copper  gauze,  nearly  pure  nitrogen 
results  (Figs.  63  and  64).  The  reason  for  the  use  of 
copper  is  that  its  oxide  is  a  non- volatile  solid.  Nitrogen 

221 


222 


NITROGEN  AND   THE  ATMOSPHERE 


Air-*-*; 


Copper 


prepared  from  air  always  contains  argon  and  other  im- 
purities. 

The  oxidation  of  ammonia  is  a  convenient  method  for 
preparing  pure  nitrogen.  Ammonia  gas  is  passed  over 
strongly  heated  cop- 
per oxide.  The  hy- 
drogen is  oxidized  to 
water,  and  the  nitro- 
gen remains.  Heat 
alone  will  liberate  ni- 
trogen from  some  of 
its  compounds.  Am- 
monium nitrite,  gen- 
tly heated,  decom- 
poses into  water  and  nitrogen.  Owing  to  the  unstable 
nature  of  ammonium  nitrite,  a  mixture  of  ammonium 
chloride  and  sodium  nitrite  is  used: 


FIG.  63.  —  PREPARATION  OF  NITROGEN. 


NH4C1  +  NaNO2 
NH4NO2- 


NaCl  +  NH4NO2 


N 


2  H20 


226.  Physical  Properties.  —  Nitrogen  is  slightly  lighter 
than  air,  as  we  should  expect  from  the  fact  that  oxygen, 
the  other  chief  constituent,  is  heavier.  It  is  without 
color,  odor,  or  taste.  Nitrogen  is  less  soluble  in  water 
than  oxygen,  so  that  the  bubbles  of  gas  given  off,  when 
ordinary  water  is  warmed,  contain  a  smaller  proportion  of 
nitrogen  than  air.  Cooled  to  a  very  low  temperature 
under  pressure,  nitrogen  becomes  a  colorless  liquid.  This 
liquefaction  is  used  commercially  in  the  preparation  of 
both  oxygen  and  nitrogen  from  the  air.  The  nitrogen  of 
liquid  air  boils  off  before  the  oxygen,  because  the  nitrogen 
has  a  lower  boiling  point.  On  further  cooling,  the  liquid 
nitrogen  freezes  to  a  white  solid. 


ACTION   WITH  HYDROGEN  223 

CHEMICAL  PROPERTIES 

227.  Inactivity.  —  The  large  amount  of  nitrogen  in  the 
air  is  due  to  its  inertness;  it  does  not  combine  readily 
with  many  substances,  and  its  compounds  are  easily  de- 
composed.    The  bulbs  of  some  incandescent  lamps  con- 
tain nitrogen.     It  unites  directly  with  few  elements  and 
with  these   only  at   high   temperatures;    sometimes   the 
electric  spark  is  necessary  to  cause  combination.     The 
ease  and  violence  with  which  its  compounds  decompose  is 
well  illustrated  by  nitroglycerine  and  guncotton. 

While  nitrogen  does  not  react  readily,  many  reactions 
are  affected  by  its  presence.  Thus  burning  cannot  be 
so  vigorous  in  air  as  in  oxygen,  since  the  large  propor- 
tion of  nitrogen  dilutes  the  oxygen,  preventing  a  rapid 
contact  with  the  combustible  material.  Some  heat  is  also 
employed  in  raising  the  temperature  of  the  nitrogen ;  the 
temperature  of  combustion  is  lower  than  would  be  the 
case  were  nitrogen  absent. 

228.  Action  with  Oxygen.  —  Nitrogen  may  be  caused  to 
combine  slowly  with  oxygen  by  passing  electric  sparks 
through  the  mixture  and  removing  the  oxides  by  dissolv- 
ing them  in  water  as  fast  as  they  are  formed.     If  they 
were  not  so  removed,  they  would  be  decomposed  by  the 
heat  of  the  succeeding  sparks.     Nitrogen  will  not  burn  in 
oxygen  without  a  continual  supply  of  external  energy, 
as  the  temperature  of  the  combustion  is  lower  than  the 
kindling  point  of  nitrogen. 

229.  Action  with  Hydrogen. — Ammonia  (NH3)  can  be 
formed  by  the  passage  of  sparks  through  a  mixture  of 
hydrogen  and  nitrogen,  or  by  employing  a  catalytic  agent. 
In  this  case,  as  in  the  similar  production  of  the  oxide,  the 


224  NITROGEN  AND   THE  ATMOSPHERE 

ammonia  must  be  removed  as  formed,  since  the  reaction  is 
reversible  and  a  point  of  equilibrium  is  reached,  at  which 
it  proceeds  as  rapidly  in  one  direction  as  in  the  other  : 


230.  Nitrides.  —  A  number  of  nitrides  are  known  ;  they 
are  made  by  heating  the  metal  with  nitrogen.     Aluminum 
nitride  is  at  present  the  most  important.     It  reacts  with 
water  : 

A1N  +  3  H2O  —  >-  A1(OH)3  +  NH3 

If  calcium  carbide  is  heated  with  nitrogen,  they  combine, 
forming  calcium  cyanamid  : 

CaC2  +  N2—  ^CaN2C  +  C 

This  is  valuable  as  a  fertilizer  and  as  a  source  of  ammonia: 
CaN2C  +  3  H20  —+  CaCO3  +  2  NH3 

231.  Composition  of  the  Air.  —  The.  average  proportions 
of  the  chief  constituents  of  the  air  are  as  follows  : 

COMPOSITION 
By  volume  By  weight 

Nitrogen     .     .     .  '   .  78.06  75.5 

Oxygen       ....  21.00  23.2 

Argon    .....  0.94  1.3 

Carbon  dioxide    .     .  0.04  0.05 

Traces  of  other  substances  are  often  present,  but  under 
the  term  air  we  usually  include  only  the  nitrogen,  oxy- 
gen, and  argon.  The  relative  amounts  of  these  are  prac- 
tically constant,  except  in  certain  localities,  as  in  cities, 
and  in  poorly  ventilated  places. 

The  molecular  motion  of  the  gases,  and  the  winds  suf- 
fice to  keep  the  composition  of  the  atmosphere  practically 


AIR  IS  A   MIXTURE 


225 


constant.  Local  conditions  may  slightly  affect  the  com- 
position, especially  in  ill-ventilated  places,  but  the  total 
quantity  of  the  air  is  so  great  —  15  pounds  resting  on  each 
square  inch  of  the  earth  —  that  even  a  large  city  produces 
scarcely  any  noticeable  effect  on  the  composition. 

The  constituents  of  air  may  be  successively  removed, 
so  as  to  leave  the  nitrogen,  by  the  apparatus  represented 
in  Fig.  64.  The  bottle  (a)  serves  as  an  aspirator  to  draw 
air  through  the  apparatus  and  also  to  collect  the  residual 
nitrogen.  The  oxygen  is  removed  by  combining  it  with 
copper  (gauze)  in  the  hard  glass  tube  (c),  which  is  heated 
by  the  combustion  furnace  (b).  Before  reaching  the  com- 


d  d  e    e 


FIG.  64.  —  SEPARATION  OF  THE  COMPONENTS  OF  AIR. 

bustion  tube,  however,  the  air  has  to  pass  through  the 
bottles  (ee)  containing  a  concentrated  solution  of  potas- 
sium hydroxide  to  take  out  the  carbon  dioxide,  and 
through  the  bottles  (dc?)  containing  concentrated  sul- 
phuric acid  to  remove  the  water  vapor  and  ammonia.  The 
nitrogen  collected  in  (a)  is  purer  than  that  obtained  by 
method  shown  in  Fig.  62. 


232.  Air  is  a  Mixture. — Air  was  once  regarded  as  an 
element ;  even  now  it  is  customary  to  refer  to  it  as  a  sin- 
gle substance.  Air  differs  from  a  compound  in  several 
important  particulars. 

(1)  If  air  is  cooled  under  pressure,  it  is  found  that  the 
oxygen  liquefies  before  the  nitrogen,  and,  conversely,  if  the 


226  NITROGEN  AND    THE  ATMOSPHERE 

liquid  air  is  allowed  to  evaporate,  the  nitrogen  vaporizes 
more  rapidly  than  the  oxygen.  If  air  were  a  compound, 
it  would  have  a  definite  boiling  point,  at  which  it  would 
vaporize  unchanged. 

(2)  If  air  is  allowed  to  pass  through  an  unglazed  por- 
celain tube,  it  is  found  that  the  lighter  nitrogen  passes 
through  the  porcelain  walls  more  rapidly  than  the  oxygen  ; 
were  they  combined  in  molecules  of  a  compound,  they 
would  go  through  with  equal  velocities. 

(3)  When  air  is  brought  in  contact  with  water,  nitrogen 
and  oxygen  dissolve  in  the  proportion  of  63  :  34 ;  while  in 
atmospheric  air  the  proportion  is  about  4  : 1  by  volume. 

(4)  If  oxygen  and  nitrogen  are  mixed  in  the  propor- 
tion in  which  they  are  found  in  the  atmosphere,  there  is 
no  evidence  of  reaction.     We  have  found  that   when  a 
chemical  change  takes  place,  there  is  usually  a  change 
in  the  temperature  caused  by  the   absorption  or  libera- 
tion of  heat.     Other  energy  changes,    such  as  the   pro- 
duction of  light  and  sound  (explosions),  often  accompany 
reactions.     None  of  these  energy  changes  occur  in  this 
case,  hence  there  is  no  probability  of  a  reaction. 

(5)  The  composition  is  not  absolutely  uniform.     While 
the  differences  in  composition  are  slight,  they  are  greater 
than  those  found  in  different  samples  of  a  chemical  com- 
pound. 

233.  "Water  Vapor  of  the  Air.  —  Some  water  vapor,  de- 
rived from  evaporation,  is  always  present  in  the  air ;  the 
amount  usually  increases  with  the  temperature  ;  thus  warm 
breezes  blowing  over  bodies  of  water  are  moist.  When 
cooled,  the  vapor  may  condense  as  fog  or  rain.  The  air 
in  desert  regions,  though  warm,  is  dry,  because  the  air 
before  being  warmed  has  passed  over  a  cool,  mountainous 
region  and  has  deposited  its  moisture. 


CARBON  DIOXIDE  AND  NITROGEN  CYCLES     227 

The  amount  of  water  in  the  air,  relative  to  the  amount 
necessary  to  saturate  the  air  under  given  conditions,  is 
known  as  the  relative  humidity.  This  is  high  when  the 
air  is  nearly  saturated,  and  low  when  the  air  is  very 
dry. 

If  the  air  is  warm,  evaporation  is  hastened.  If,  how- 
ever, the  air  is  moist,  evaporation,  as  from  the  skin  and 
lungs,  is  retarded  and  we  feel  close,  oppressed,  and  un- 
comfortable. If  the  air  is  dry,  although  warm,  we  note 
the  cooling  effect  of  the  hastened  evaporation.  In  cool 
weather  we  are  still  sensible  to  the  moisture.  Only  a  very 
small  amount  of  water  vapor  is  required  to  make  a  crisp, 
bracing  atmosphere  become  clammy  and  disagreeable. 

When  the  air  is  nearly  half  saturated,  it  is  most  com- 
fortable. In  crowded  rooms  it  is  usually  too  moist,  and 
unfortunately  there  is  no  simple  means  by  which  the 
moisture  in  the  room  can  be  reduced.  On  a  large  scale 
moisture  is  most  readily  removed  by  cooling  and  condens- 
ing the  water  vapor. 

234.  Carbon  Dioxide  and  Nitrogen  Cycles.  —  Carbon  di- 
oxide is  always  present  in  the  air,  though  in  a  very  small 
proportion.  In  normal  outdoor  air  about  4  parts  in 
10,000,  or  four  hundredths  of  1  %,  are  present.  The  pro- 
portion may  rise  rather  high  in  a  crowded  room  from  the 
exhalations  of  the  people  present.  Carbon  dioxide  is 
continually  given  off  to  the  air  in  the  exhalations  of 
animals  and  in  combustion,  but  as  it  is  taken  up  from  the 
air  by  plants,  the  amount  in  the  air  remains  practically 
constant.  The  very  small  percentage  of  carbon  dioxide 
in  the  air  furnishes  all  the  carbon  needed  for  the  growth 
of  plants. 

The  oxygen  in  the  air  is  removed  by  animals  and  re- 
placed by  plant  life ;  thus  the  plant  and  animal  life  pre- 


228  NITROGEN  AND   THE  ATMOSPHERE 

serve  the  balance,  maintaining  the  atmosphere  at  a  constant 
composition. 

The  nitrogen  removed  from  the  air  to  form  soluble 
compounds  in  the  soil,  is  taken  up  by  plants  and  con- 
verted into  proteins.  These  proteins  are  the  source  of  the 
protoplasm  of  animals.  These  unstable  proteins  break  up 
both  during  the  life  of  the  plants  and  animals  and  after 
their  death,  and  the  nitrogen  finally  makes  its  way  back 
to  the  air. 

235.  Other  Constituents  of  the  Air.  —  Other  materials  are 
found  in  small  amounts :    argon,  helium,  and  other  inert 
gases  (about  1  %),  traces  of  ammonia,  sulphur  compounds, 
and  fine  dust  particles,  which  depend  on  local  conditions 
and    often    produce  climatic  effects.     These    dust   parti- 
cles include  a  great  variety  of  materials  —  steel,  stone, 
soil,  and  coal  dust.     The  organic  particles  include  pollen 
grains  and  spores  of  plants,  germs  of  disease,  which  are 
always  present,  shreds  of  various  fabrics,  as  cotton  and 
woolen  cloth,  and  dried  bits  of  refuse  of  all  sorts. 

f- 

THE  INERT  GASES 

236.  Discovery  of  Argon.  —  The  discovery  and  investi- 
gation of  the  inert  gases  in  the  air  have  afforded  one  of 
the  most  brilliant  and  interesting  chapters  in  the  history 
of   chemistry.     In  1892   Rayleigh,  an  English  scientist, 
noticed  that  nitrogen  from  the  air  was  a  trifle  heavier 
than  that  obtained  from  nitrogen  compounds.     This  meant 
that  the  supposedly  pure  nitrogen  from  the  air  contained 
some  gas,  heavier  than  nitrogen,  which  had  remained  un- 
detected despite  the  careful  study  of  the  atmosphere  for 
more  than  a  century. 

A   small   amount  of    the   hitherto   unknown   eras   was 

O 

obtained   by  Ramsay,  an   English   chemist,  who   passed 
nitrogen  from  the  air  over  heated  magnesium  which  com- 


Sir  William  Ramsay  was  born  in  Glasgow,  Scotland,  in  1852. 
He  shared  with  Rayleigh  the  honor  of  the  discovery  of  argon. 
This  element,  although  present  in  the  atmosphere  to  the  extent  of 
about  one  per  cent,  had  escaped  detection  because  of  its  chemical 
inactivity.  Ramsay  is  a  remarkably  skillful  experimenter.  Ram- 
say's other  work  has  been  to  show  the  presence  of  other  previously 
undiscovered  gases  in  small  amount  in  the  atmosphere ;  to  show 
that  helium,  formerly  known  only  as  a  constituent  of  the  sun, 
was  given  off  by  certain  minerals ;  and  to  show,  with  Soddy,  that 
helium  is  one  of  the  decomposition  products  of  radium.  Ramsay 
was  awarded  the  Nobel  Prize  in  1904. 


THE  INERT  GASES  229 

bined  with  the  nitrogen,  forming  magnesium  nitride,  a 
yellowish  solid.  This  method  yielded  but  a  trace  of  the 
new  gas,  and  a  better  way  was  soon  devised  by  Lord 
Rayleigh.  Even  this  improved  method,  however,  was  slow 
and  many  precautions  were  necessary,  in  order  to  secure  a 
very  small  sample  of  the  new  material. 

The  new  substance  was  found  to  constitute  about  1  % 
of  the  air.  It  is  one  fourth  heavier  than  oxygen  and 
over  one  third  heavier  than  nitrogen.  All  attempts  to 
make  the  gas  enter  into  chemical  combination  failed,  and 
hence  it  was  given  the  name  argon,  signifying  inactive. 

237.  Isolation  of  the  Other  Inert  Gases.  —  Certain  irregu- 
larities in  the  properties  of  argon  led  Rayleigh  and  Ram- 
say to  suspect  that  this  new  gas  was  not  itself  pure.     By 
means  of  liquid  air  the  argon  obtained  from  the  atmos- 
phere was   liquefied,  and,  at  the  low   temperatures  ob- 
tained, repeated  processes  of  fractional  evaporation  and 
liquefaction  were  carried  on.     The  argon  was  found  to 
contain  minute  amounts  of  other  inert  gases.     Two  of 
these  could  be  separated  only  by  using  the  extremely  low 
temperature  possible  with  liquid  hydrogen.     Three  of  the 
new  inert  gases  were  given  names  which  bring  to  mind 
the  long,  baffling  search  for  them.     Neon  means  new; 
xenon,   stranger ;    and    krypton,   hidden.      Besides   these 
three  gases  a  trace  of  helium  was  found.     This  element 
was  formerly  supposed  to  exist  only  in  the  sun. 

238.  Properties. — Neon,    xenon,    krypton,    and    niton 
(§  553)  closely  resemble  argon,   but  each  was  found  to 
have  its  peculiar  spectrum  and  all  except  neon  have  a  very 
low  but  definite  boiling  point.     Thus  they  are  elements  and 
form  a  very  closely  related  group  with  argon.     Certain  con- 
siderations have  led  us  to  believe  that  all  these  elements 
contain  but  one  atom  to  the  molecule.     Their  inertness 


230  NITROGEN  AND   THE  ATMOSPHERE 

with  respect  to  chemical  combination  explains  why  no 
compounds  containing  them  are  known,  and  why  they 
were  overlooked  until  recently. 

239.  Helium.  —  In  1869  Lockyer  noticed  some  lines  in 
the  sun's  spectrum  which  did  not  correspond  with  those 
of  any  element  found  on  earth.  In  1895  Ramsay,  in 
searching  for  sources  of  argon,  examined  the  gases  given 
off  by  certain  .rare  minerals  when  heated.  In  the  case 
of  clevite,  a  gas  was  obtained  which  gave  a  spectrum 
identical  with  that  of  the  supposed  element  in  the  sun,  and 
hence  was  given  the  name  helium.  The  new  element  has 
since  been  obtained  from  the  waters  of  certain  mineral 
springs  and  has  been  found  to  exist  in  minute  quantities 
in  the  atmosphere. 

Helium  is  a  very  light  gas,  being  only  twice  as  heavy 
as  hydrogen.  Its  properties  resemble  those  of  argon,  and 
it  is  therefore  classed  with  the  other  inert  gases. 

Recent  researches  have  proved  that  helium  results  from 
the  decomposition  of  radium,  which  is  considered  to  be  an 
element  (see  Chapter  XL). 

SUMMARY 

Nitrogen  constitutes  the  larger  part  of  the  air.  It  is  a  constituent 
of  protoplasm  and  of  proteins,  hence  is  essential  to  vital  processes. 

It  is  prepared  by 

( 1 )  the  oxidation  of  ammonium  compounds ; 

(2)  removing  the  oxygen  from  the  air  by  phosphorus ;  this  is 

sufficiently  pure  for  ordinary  use. 

One  liter  of  nitrogen  weighs  1 .26  grams.  Its  atomic  weight  is  1 4. 
The  nitrogen  molecule  contains  2  atoms  (N2). 

Nitrogen  is  generally  inert ;  under  electric  stress  it  reacts  slowly 
with  oxygen  and  with  hydrogen.  A  few  bacteria  are  capable  of 
assimilating  it. 


EXERCISES 


231 


Air  is  essentially  nitrogen,  oxygen,  and  argon,  with  varying 
amounts  of  water  vapor,  carbon  dioxide,  and  compounds  of  nitro- 
gen and  sulphur. 

The  amount  of  the  air  is  so  enormous  that  local  conditions  have 
little  or  no  appreciable  effect  on  its  composition.  The  important 
factor  determining  the  composition  is  the  balance  maintained  be- 
tween plant  and  animal  life. 

OXYGEN-CARBON  DIOXIDE  CYCLE 

Oxygen 


PLANT 
STRUCTURE 


AIR 


ANIMAL 
STRUCTURE 


AIR 


Carbon 
dioxide 

NITROGEN  CYCLE 
WATER  1 


Oxygen 
Nitrogen 


Nitrates 


PLANT 
STRUCTURE 


Ammonia 


ANIMAL 
STRUCTURE 


The  variation  in  composition  indicates  that  air  is  merely  a 
mixture.  Chemical  reactions  are  always  accompanied  by  thermal 
changes,  and  there  are  no  such  changes  on  mixing  the  constituents 
of  air. 

EXERCISES 

1.  Why  axe  so  few  mineral  compounds  of  nitrogen  found  in 
nature  ? 

2.  How  was  it  shown  that  the  material  in  the  air,  formerly 
known  as  .nitrogen,  was  not  a  pure  substance  ? 


232  NITROGEN  AND    THE  ATMOSPHERE 

3.  What  chemical  reactions  take  place  in  the  air  during  a 
thunderstorm  ? 

4.  From  what  sources  are  the  principal  constituents  of  the 
air  continually  derived  ?     By  what  means  are  they  removed  ? 
Why  is  the  composition  of  the  air  so  nearly  constant  all  over 
the  earth  ? 

5.  What  is  the  weight  of  air  over  a  city  lot  25  x  100  ft.  ? 
How  much  of  it  is  oxygen  ? 

6.  State  the  ratio  by  volume  of  the  two  principal  constit- 
uents of  the  air.     How  may  this  ratio  be  determined  ?     Men- 
tion  in   regard  to  one  of   those   constituents  two  important 
functions  in  nature. 

7.  Name  four  common  substances  present  in  the  air.     How 
could  you  show  the  presence  of  each  ? 

8.  Give  two  proofs  that  air  is  a  mixture  rather  than  a 
chemical  compound.     State  how  it  could  be  proved  by  chemi- 
cal means  that  air  contains  (a)  water,  (6)  carbon  dioxide. 

9.  Name  four  gases  always  present  in  the  air.     By  what 
natural  process  is  each  removed  from  the  air  ? 

10.  What  change  would  take  place  if  each  of  the  following 
substances  was  left  in  an  open  vessel :    (a)  sodium,  (6)  anhy- 
drous calcium  chloride,  (c)  lime  water,  (d)  crystals  of  washing 
soda,  (e)  concentrated  sulphuric  acid  ? 

11.  Name  three  of  the  rare  and  inert  gases  and  state  where 
they  may  be  found.     What   peculiar  property  is  shown   by 
radium  ? 


CHAPTER   XXII 

NITROGEN  COMPOUNDS 
AMMONIA 

240.  Natural  Formation.  —  The  most  important  constitu- 
ent of  all  living  organisms  is  protoplasm,  a  complex  sub- 
stance containing  nitrogen,  carbon,  hydrogen,  oxygen,  and 
other  elements.     When  a  plant  or  animal  dies  and  decom- 
position sets  in,  the  protoplasm  breaks  up  very  quickly, 
yielding   simpler  compounds.     The  nitrogen  unites  with 
the   hydrogen   to   form  the  gas  ammonia   (NH3).      The 
characteristic  odor  of  ammonia  can  often  be  noted  in  the 
vicinity  of   heaps   of   decomposing   animal   or  vegetable 
refuse. 

241.  Commercial  Preparation.  —  Ammonia    is    obtained 
commercially  as  one  of  the  products  of  the  destructive 
distillation  of  coal,  in  the  manufacture  of  coal  gas  and  coke. 
Soft  coal  is  heated  in  iron  retorts  at.  an   intense  heat. 
Moisture,  volatile  matter,  and  gases  are  driven  off,  and  coke 
remains  in  the  retort.     The  gases  are  cooled  in  pipes,  and 
coal  tar   is  extracted,  then  the  gases  are  passed  into  a 
"scrubber,"    where    they   come   in    contact   with    water, 
and  here  the  ammonia  dissolves.     The  water  containing 
ammonia  compounds  is  boiled  with  milk  of  lime,  and  the 
expelled   ammonia  is  passed   into  sulphuric  acid;    tarry 
materials  are  separated,  and  the  solution  of  ammonium 
sulphate  is  evaporated  and  crystallized. 

The  dried,  crystallized  ammonium  sulphate  is  mixed 


234  NITROGEN  COMPOUNDS 

with  slaked  lime  in  an  iron  retort  and  heated.     Ammonia 
gas  and  water  are  given  off,  and  calcium  sulphate  remains: 

Ca(OH)2  +  (NH4)2SO4^±CaSO4  +  2  H2O  +  2  NH3 

The  ammonia  may  be  dissolved  in  water,  forming  ammonia 
water,  or  spirits  of  hartshorn,  or  it  may  be  dried  by  passing 
through  quicklime  (CaO)  and  compressed  in  tanks. 

The  possibility  of  utilizing  the  free  nitrogen  of  the 
atmosphere  in  the  manufacture  of  ammonia  has  appealed 
to  many  chemists.  At  present,  two  processes  for  accom- 
plishing this  bid  fair  to  become  of  considerable  commercial 
importance : 

1.  Haber  and  Le  Rossignol  process. 

Nitrogen  and  hydrogen  are  caused  to  combine  at  a 
suitable  temperature  (500°-700°  C.)  and  pressure  (50 
-100  atmospheres)  in  the  presence  of  a  catalytic  agent: 

N2  +  3  H2  ^±  2  NH3 

A  state  of  equilibrium  is  reached  when  the  gas  mixture 
contains  only  a  small  per  cent  of  ammonia.  The  ammonia 
is  removed  from  the  mixture,  and  the  remainder,  with  a 
new  mixture  of  hydrogen  and  nitrogen,  is  again  passed 
through  the  apparatus. 

2.  Ostwald  process. 

Calcium  cyanamid  is  prepared  by  passing  nitrogen, 
obtained  from  air,  over  hot  calcium  carbide: 

CaC2  +  N2  — >-  CaN2C  +  C 

The  calcium  cyanamid  is  then  treated  with  steam  under 
a  pressure  of  from  6  to  8  atmospheres : 

CaN2C  +  3  HfcO  — *-  CaCO3  +  2  NH3 


PREPARATION  OF  AMMONIA 


235 


242.  Laboratory  Preparation.  —  Ammonia  is  usually  pre- 
pared (Fig.  65)  by  heating  ammonium  chloride  (sal 
ammoniac)  with  calcium  hydroxide  (slaked  lime)  : 

Ca(OH)2  +  2  NH4C1  —  >-  CaCl2  +  2  NH8  +  2  H2O 

In  this  preparation,  any  ammonium  salt  can  be  substituted 
for  ammonium  chloride,  and  any  non-volatile  base  for  the 
calcium  hydroxide.  A  typical  reaction  probably  proceeds 
as  follows  : 


Na2SO4 
2  NH 


2  NH4OH 


2  H2O 


(NH4)2S04  +  2  NaOH 
2  NH4OH 

the  complete  reaction  being  represented  by  the  equation: 
(NH4)2S04  +  2  NaOH  —  >-  N^SO,  +  2  NH8  +  2  H2O 

That  is,  ammonium  hydroxide 
is  first  formed  and  breaks  up  at 
once  into  ammonia  and  water. 
Since  ammonia  is  a  gas,  a  volatile 
product  can  be  formed  as  a  re- 
sult of  the  reaction  between  am- 
monium salts  and  bases.  This 
is  analogous  to  the  fact  that 
many  acids  are  formed  by  the 
action  of  sulphuric  acid  upon 
their  salts,  because  they  have 
lower  boiling  points  than  sul- 
FlG>  65<  phuric  acid. 

Ammonia  can  also  be  obtained  by  warming  a  strong 
ammonium  hydroxide  solution: 

NH4OH 


243.  Physical  Properties.  —  Ammonia  is  a  colorless  gas 
possessing  a  characteristic,  pungent,  overpowering  odor. 


236 


NITROGEN  COMPOUNDS 


It  is  lighter  than  air,  and  exceedingly  soluble  in  water. 

At  0°  C.  one  volume  of  water  will  hold  in  solution  over 
1000  volumes  of  the  gas;  at  ordinary  tem- 
peratures about  700  volumes.  This  solu- 
tion is  known  as  ammonia  water,  or  am- 
monium hydroxide.  On  being  heated  or 
on  standing  exposed  to  air,  it  gives  off 
ammonia. 

The  great  solubility  of  this  gas  is  strik- 
ingly shown  by  the  "ammonia  fountain" 
(Fig.  66).  A  flask  is  filled  with  dry  am- 
monia, and  inverted  over  water.  As  soon 
as  the  ammonia  comes  in  contact  with  the 
water,  the  gas  rapidly  dissolves  and  water 
rushes  in,  forming  a  fountain.  Ammonia 
is  easily  liquefied;  at  ordinary  tempera- 
tures a  pressure  of  about  4.5  atmospheres 
FIG.  66.  is  needed. 

244.  Chemical  Properties.  —  Pure,  dry  ammonia  is  not  an 
active  substance;  it  is  not  readily  combustible  in  air,  but 
can  be  burned  in  oxygen.  When  ammonia  is  passed  over 
heated  copper  oxide,  water  and  nitrogen  are  obtained: 

2  NH3  +  3  CuO  — »-  3  Cu  +  3  H2O  +  N2 

•  The  most  important  chemical  property  of  ammonia  is 
the  basic  character  of  its  water  solution.  This  solution, 
which  is  often  incorrectly  called  ammonia,  turns  red 
litmus  blue,  neutralizes  acids,  and  conducts  electricity;  it 
behaves  like  a  solution  of  a  base.  We  may  assume,  there- 
fore, the  existence  of  OH~~  ions  in  the  solution  of  ammonia. 
When  this  solution  is  neutralized  with  hydrochloric  acid, 
a  salt  is  formed  whose  composition  is  represented  by  the 
formula  NH4C1.  Similar  salts  are  formed  with  other 


USES   OF  AMMONIA  237 

acids.  The  group  NH4  is  known  as  the  ammonium  radical. 
A  water  solution  of  ammonia,  then,  contains  the  base 
ammonium  hydroxide  which  reacts  with  acids  to  form  salts: 

NH4OH  +  HC1  — ^  H20  +  NH4C1 
2  NH4OH  +  H2S04  — >-  2  H2O  +  (NH4)2SO4 

245.  Ammonia  Water.  —  Ammonia  water  contains  both 
ammonia  and  ammonium  hydroxide  in  solution;  the  ammo- 
nia, water,  and  ammonium  hydroxide,  being  in  a  state  of 
equilibrium: 

NH3  +  H2O^±NH4OH 

The  alkaline  properties  of  ammonia  water  are  due  to  the 
fact  that  the  ammonium  hydroxide  present  dissociates, 
yielding  l^droxyl  (OH~)  ions: 

NH4OH^±NH4+  +  OH- 

Ammonia  water  is  commonly  kept  in  rubber-stoppered 
bottles  because  concentrated  solutions  of  ammonia  cause 
cork  to  disintegrate  rapidly,  and  they  attack  glass  so  as  to 
make  it  difficult  to  remove  a  glass  stopper  without  break- 
ing the  bottle. 

The  value  of  ammonia  as  a  cleansing  agent  is  due  to  its 
ability  to  dissolve  grease.  Its  basic  properties  give  it  a 
use  in  the  laboratory,  whenever  a  volatile  alkali  is  desirable. 
Household  ammonia  is  prepared  by  adding,  in  quantity 
not  to  exceed  6  %,  oleic  acid  to  ammonia  water.  Cloudy 
ammonias  contain  soap  and  frequently  other  ingredients. 

246.  Uses  of  Ammonia.  —  The  most  important  uses  of 
ammonia  are  as  a  refrigerating  agent  and  for  the  prepara- 
tion of  ammonia  water.     When  a  gas  is  liquefied,  heat  is 
liberated,  and  when  the  liquid  returns  to  the  gaseous  state, 
heat  is  absorbed.     In  one  process  for  the  manufacture  of 


238 


NITROGEN  COMPOUNDS 


artificial  ice  (Fig.  67),  ammonia  is  compressed  by  power- 
ful pumps;  it  is  then  cooled  and  liquefied  by  passing 
cold  water  over  the  pipes  containing  the  compressed  gas. 
The  liquid  ammonia  is  allowed  to  evaporate  rapidly  in 
pipes  immersed  in  a  concentrated  solution  of  salt  or  cal- 
cium chloride.  The  ammonia  in  passing  from  the  state  of 
a  liquid  to  that  of  a  gas  takes  heat  from  the  salt  solution 
and  cools  it  to  a  point  below  the  freezing  point  of  pure 


FIG.  67. —  REFRIGERATING  PLANT. 

water.  Cans  of  water  are  placed  in  the  cold  brine,  and 
the  water  is  frozen  in  from  24  to  36  hours.  Cold-storage 
rooms  may  be  kept  cool  by  distributing  the  cold  brine  to 
the  apartments  to  be  cooled,  where  it  is  passed  through 
coils  near  the  ceiling. 

Large  quantities  of  ammonia  are  used  in  the  manufac- 
ture of  sodium  carbonate  by  the  Solvay  process. 

247.  Ammonium  Salts.  —  Although  ammonium  has  never 
been  obtained  in  a  free  state,  there  are  a  large  number  of 
ammonium  salts. 


NITROUS  OXIDE  239 

Ammonium  salts  react  similarly  to  the  compounds  of 
sodium  and  potassium,  and  they  may  be  considered  as 
substances  in  which  the  group  of  atoms  NH4  (ammonium 
radical)  takes  the  same  part  as  an  atom  of  hydrogen  or 
potassium.  Thus  as  potassium  chloride  dissociates  into 
K+  and  Cl~  ions,  ammonium  chloride,  NH4C1,  dissociates 
into  NH4  and  Cl~  ions. 

If  an  electric  current  is  passed  through  a  solution  of 
ammonium  chloride,  we  might  expect  to  obtain  ammo- 
nium and  chlorine,  since  these  are  the  ions  formed.  The 
chlorine,  however,  liberated  at  the  anode  reacts  with  the 
ammonium  salt  present  in  the  solution,  forming  hydro- 
chloric acid  and  nitrogen.  At  the  cathode,  the  NH~J  ion, 
on  discharging,  decomposes  into  ammonia  and  hydrogen, 
the  ammonia  dissolving  in  the  water. 

OXIDES  OF  NITROGEN 

Nitrogen  combines  with  oxygen  in  five  proportions,  cor- 
responding to  the  formulas  :  N2O,  nitrous  oxide ;  NO, 
nitric  oxide ;  N2O3,  nitrous  anhydride ;  NO2,  nitrogen 
peroxide  ;  N2O5,  nitric  anhydride. 

248.  Nitrous  Oxide.  —  Nitrous  oxide  (N2O),  laughing 
gas,  is  prepared  by  heating  ammonium  nitrate  (Fig.  68)  : 

NH4N08— *.N2O  +  2  H20 

The  nitrate  melts  and  soon  begins  to  decompose  with 
effervescence.  The  heat  must  be  carefully  regulated  or 
an  explosion  may  occur.  The  nitrous  oxide  is  a  colorless 
gas  with  a  slightly  sweet  taste.  When  inhaled,  it  produces 
unconsciousness  and  is  used  for  this  purpose  in  minor 
surgical  operations.  It  was  the  first  of  modern  anesthetics 
and  was  discovered  by  Sir  Humphry  Davy. 

Nitrous  oxide  supports  combustion  almost  as  well  as 


240 


NITROGEN  COMPOUNDS 


oxygen,  but,  unlike  oxygen,  it  does  not  react  with  nitric 
oxide,  nor  does  it  support  the  combustion  of  sulphur  which 
is  not  burning  vigorously. 


FIG.  68.  —  PREPARATION  OF  NITROUS  OXIDE. 

a,  flask  containing  melted  ammonium  nitrate ;   b,  catch  bottle  for  water 
formed  ;  c,  collecting  bottle. 

249.  Nitric  Oxide.  —  Nitric  oxide  is  a  colorless  gas ;  it  is 
generally  formed  in  the  action  of  dilute  nitric  acid  with 
metals.  In  the  laboratory  copper  and  nitric  acid  are  used  : 

3  Cu  +  8  HN03— *-3  Cu(N03)2  +  2  NO  +  4  H2O 

It  does  not  support  combustion,  being  more  stable  than 
nitrous  oxide,  but  readily  combines  with  oxygen,  forming 
nitrogen  peroxide,  with  a  slight  rise  of  temperature : 


2NO  +  O, 


2  NO, 


This  action  makes  it  useful  as  a  catalytic  agent  in  the 
chamber  process  for  the  manufacture  of  sulphuric  acid 
(§  216). 


OTHER   OXIDES 


241 


250.  Nitrogen  Peroxide.  —  Nitrogen  peroxide,  NO2,  is  a 
heavy  red-brown  gas  of  disagreeable  odor.  It  is  formed 
immediately  whenever  nitric  oxide  is  brought  in  contact 
with  oxygen  or  with  air  (Fig.  69).  It  dissolves  in 
water,  the  solution  has  an  acid  reaction,  and  contains 
nitrous  and  nitric  acids  : 


2  NO 


H2O 


HNO  +  HNO 


a 


Thus  the  fumes  from  nitric  acid,  containing  oxides  of 
nitrogen,  form  nitric  acid  with  water,  and  cause  the  cor- 
rosion usually  observed  on 
metal  objects  near  which 
nitric  acid  is  kept. 

Nitrogen  peroxide  is  read- 
ily liquefied  and  solidified, 
the  liquid  being  yellow  and 
the  solid  colorless.  When 
the  liquid  vaporizes,  the 
vapor  given  off  at  the  boil- 
ing point  is  light  brown  and 
grows  darker  as  the  temper- 
ature rises.  Vapor  density 
determinations  indicate  that 
vapor  given  off  from  the  liquid  has  a  composition  represented 
by  the  formula  N2O4,  part  of  the  molecules  of  which  immedi- 
ately dissociate  into  NO2  molecules,  so  that  the  light- 
colored  gas  is  a  mixture  of  the  two  oxides.  As  the  tem- 
perature rises,  more  molecules  dissociate,  and  the  dark  gas 
at  high  temperatures  is  chiefly  NO2.  These  changes  are 
represented  by  the  equation  : 


FIG.  69.  —  NITRIC  OXIDE. 
a,  closed ;  b,  open  to  air. 


251.  Other  Oxides.  —  Nitrogen  trioxide   (N2O8)  and  ni- 
trogen  pentoxide  (N2O6)  are  unstable  substances  of  no 


242  NITROGEN  COMPOUNDS 

particular  importance.     They  unite  with  water,  forming 
nitrous  and  nitric  acids  : 

H2O  +  N2O3—  ^ 


Hence  the  trioxide  is  termed  nitrous  anhydride  and  the 
pentoxide  is  known  as  nitric  anhydride. 

NITRIC  ACID 

Nitric  acid  was  known  to  the^  alchemists,  who  called  it 
aqua  fortis  (strong  water),  because  of  the  great  chemical 
activity  it  displays.  They  prepared  it  by  lieating  a  mix- 
ture of  potassium  nitrate,  copper  sulphate,  and  potassium 
aluminum  sulphate.  The  last  two  of  these  substances 
contain  water  of  crystallization,  and  from  this  came  the 
hydrogen  which  the  acid  contains. 

252.  Preparation  from  a  Nitrate.  —  Both  commercially  and 
in  the  laboratory,  nitric  acid  is  prepared  by  heating  a 
mixture  of  sulphuric  acid  and  sodium  nitrate.  The  latter 
substance  is  found  in  considerable  quantities  in  certain 
parts  of  Chile  and  in  the  western  United  States.  Other 
nitrates  might  be  used  ;  for  instance,  potassium  nitrate, 
which  is  also  found  in  nature,  though  in  much  smaller 
quantity  than  sodium  nitrate. 

The  reaction  may  proceed  in  two  stages.  The  first  re- 
action is: 

H2S04— 


If  there  is  an  excess  of  acid  and  the  temperature  is  kept 
low,  the  reaction  does  not  proceed  beyond  this  point.  If, 
on  the  other  hand,  there  is  an  excess  of  sodium  nitrate, 
the  sodium  hydrogen  sulphate  that  is  formed  in  the  first 


PREPARATION  OF  ^NITRIC  ACID  243 

action  reacts  at  a  higher  temperature  with  more  sodium 
nitrate,  according  to  the  equation: 

NaNO3  +  NaHSO4—  -^Na2SO4  +  HNO8 

Writing  one  equation  to  show  the  final  results  of  the  two 
stages  of  the  reaction,  we  have: 


2  NaNO3  +  H2SO4—  ^Na^SC^  +  2  HNO3 

Since  the  second  action  requires  a  higher  temperature 
than  the  first,  and  since  nitric  acid  undergoes  considerable 
decomposition  at  the  higher  temperature,  it  is  customary 
to  use  enough  sulphuric  acid  to  give  only  the  first  reaction. 
Sulphuric  acid  is  used  in  this 
operation  for  the  reason  that  its 
boiling  point  is  higher  than  that 
of  nitric  acid.  Very  few  acids 
could  be  substituted  for  sulphuric 
acid  because  most  of  them  have 

too   low  boiling  points.     In   the    "~ 

FIG.  70. 
laboratory   preparation   of    nitric 

acid,  the  distilled  acid  is  usually  collected  in  a  test  tube 
or  other  receiver,  kept  cool  by  water  in  a  battery  jar 
(a,  Fig.  70). 

Nitric  acid  is  an  important  article  of  commerce;  so 
the  reaction  that  has  been  described  is  carried  out  on  a 
large  scale.  Iron  retorts  are  used,  and  the  acid  is  con- 
densed and  collected  in  a  series  of  earthenware  vessels. 

253.  Preparation  from  Air.  —  Several  processes  for  em- 
ploying atmospheric  nitrogen  in  the  manufacture  of  nitric 
acid  are  in  use.  A  number  of  these  utilize  the  direct  oxi- 
dation of  atmospheric  nitrogen  by  high-tension  arc  dis- 
charges of  electricity.  Under  suitable  conditions,  small 
quantities  of  nitric  oxide  are  formed: 


244 


NITROGEN  COMPOUNDS 


Courtesy  of  Norwegian  Hydro-Electric  Co.,  RJuken. 
FIG.    71.  —  ELECTRIC    POWER    HOUSE,    RJUKEN,    NORWAY    (ABOVE),    AND 
CHEMICAL  PLANT   (BELOW),   WHERE  THE   ELECTRICITY  is   USED   IN  THE 
FIXATION  OF  NITROGEN. 


PROPERTIES   OF  NITRIC  ACID  245 

N2  +  02—  ^2  NO 

Below   600°   C.,  nitric  oxide   combines   with  oxygen   to 
form  nitrogen  peroxide: 

2  NO  +  O2—  »-2  NO2 

Nitrogen  peroxide  unites  with  water  to  form  a  mixture  of 
nitric  acid  and  nitrous  acid: 


2  N02  +  H2O—  ^HNO3  +  HNOa 

Except  in  extremely  dilute  solutions,  nitrous  acid  decom- 
poses, yielding  nitric  acid,  nitric  oxide,  and  water: 

3  HN02—  ^HN03  +  2  NO  +  H2O 

The  final  equation  is 

2H20—  ^ 


254.  Physical  Properties.  —  Nitric  acid  is  a  colorless  liquid 
at  ordinary  temperatures.     The  diluted  acid  has  boiling 
points  varying  with  the  dilution.     A  mixture  that  contains 
68%  of  pure  nitric  acid  boils  constantly  at  120°. 

As  it  is  ordinarily  prepared,  nitric  acid  contains  con- 
siderable water  and  is  colored  yellow  by  the  presence  of 
dissolved  oxides  of  nitrogen,  which  result  from  the  decom- 
position of  the  acid  by  the  heat  used  in  its  preparation. 
It  is  usual  to  distil  the  acid  in  an  apparatus  in  which  the 
pressure  is  less  than  that  of  the  atmosphere.  In  this  way 
the  distillation  can  be  carried  on  at  a  lower  temperature 
and  the  undesirable  decomposition  is  avoided. 

255.  Chemical  Properties.  —  The    chemical    behavior    of 
nitric  acid  is  very  interesting.     Generally  its  action  is  not 
a  simple  one.     This  is  because  it  possesses  two  distinct 
chemical  characteristics,  both  of   which  it  displays   in  a 
marked  degree. 


246  NITROGEN  COMPOUNDS 

First,  it  is  a  very  strong  acid.  This  is  because  it  is 
highly  dissociated  into  ions  when  dissolved  in  water,  even 
in  concentrated  solution.  The  hydrogen  ions,  being 
present  in  large  numbers,  produce  all  the  actions  that  are 
characteristic  of  acids,  such  as  the  formation  of  salts  with 
bases  and  the  transference  of  the  electric  charge  of  the 
hydrogen  ion  to  metallic  atoms,  forming  metallic  ions,  when 
the  acid  is  brought  in  contact  with  a  metal. 

Second,  nitric  acid  is  a  powerful  oxidizing  agent.  This 
can  be  shown  in  a  number  of  ways :  charcoal  can  be  made 
to  burn  in  nitric  acid ;  horsehair  will  take  fire  if  put  into 
the  gaseous  substance ;  both  the  coloring  matter  and  the 
fabric  of  cotton  or  woolen  goods  are  quickly  destroyed  by  it. 

256.  Reduction  Products.  —  When  nitric  acid  does  oxidiz- 
ing work,  it  is  itself  reduced.  There  are  various  reduction 
products  of  the  acid.  The  product  formed  depends  on  a 
number  of  conditions,  particularly  on  the  temperature  and 
the  degree  of  dilution  of  the  acid.  In  any  case,  there  are 
several  reduction  products,  though  usually  one  is  found 
in  excess  of  the  others.  If  the  acid  is  moderately  dilute, 
and  acts  at  ordinary  temperatures,  the  .reduction  product 
is  commonly  nitric  oxide.  From  concentrated  nitric  acid, 
a  large  quantity  of  nitrogen  peroxide  is  always  obtained. 
From  very  dilute  acid,  the  reduction  product  may  be 
nitrous  oxide,  hydrogen,  or  even  ammonia.  Thus  we  see 
that  the  more  dilute  the  acid,  the  farther  the  reduction  is 
carried.  This  does  not  mean  that  the  more  dilute  acid 
is  the  stronger  oxidizing  agent;  on  the  contrary,  it  is 
because  the  concentrated  acid  is  such  a  powerful  oxidizing 
agent  that  the  lower  reduction  products  cannot  escape 
from  the  acid  without  being  themselves  oxidized  to  a 
certain  extent. 

As  we  should  expect  from  its  being  so  strong  an  oxidiz- 


NITRIC  ACID    WITH  METALS  247 

ing  agent,  nitric  acid  is  a  rather  unstable  compound,  tend- 
ing to  give  up  part  of  its  oxygen  to  form  more  stable 
compounds.  It  will  do  this  under  the  influence  of  light, 
or  more  readily  if  some  oxidizable  substance  is  present. 

257.  Action  with  Metals.  — Nitric  acid  acts  with  many  of 
the  metals,  but  owing  to  its  dual  chemical  character,  it 
does  not  act  on  them  in  the  same  way  that  other  acids  do. 
Hydrogen  is  seldom  evolved  by  the  action  of  nitric  acid 
on  metals.  The  gases  that  are  given  off  are  the  reduction 
products  of  nitric  acid. 

The  action  of  moderately  dilute  nitric  acid  on  copper 
may  be  taken  as  a  type  of  its  action  on  the  heavy  metals, 
as  silver,  mercury,  and  lead.  Experiment  shows  that  the 
products  of  this  action  are  copper  nitrate,  nitric  oxide,  and 
water. 

It  is  probable  that,  as  a  result  of  the  first  stage  of  the 
action,  there  is  a  tendency  to  liberate  hydrogen,  according 
to  the  equation : 

(1)  Cu  +  2  HNO3— ^Cu(NO8)2  +  2  H 

But  the  nascent  hydrogen  is  at  once  oxidized  to  water  by 
the  nitric  acid,  and  a  part  of  the  nitric  acid  is  reduced  to 
nitric  oxide  at  the  same  time : 

(2)  3  H  +  HNO3  — ^  2  H2O  +  NO 

To  combine  equations  (1)  and  (2),  we  should  consider 
that  only  two  atoms  of  hydrogen  were  produced  in  equa- 
tion (1),  while  three  atoms  of  hydrogen  were  consumed 
in  equation  (2).  The  hydrogen  could  not  have  been  con- 
sumed more  rapidly  than  it  was  produced.  If  it  had  been 
produced  more  rapidly  than  it  was  consumed,  free  hydro- 
gen would  have  appeared.  To  satisfy  these  conditions, 


248  NITROGEN  COMPOUNDS 

we  multiply  equation  (1)  by  3,  and  equation  (2)  by  2,  so 
that  they  become  respectively  : 

3  Cu  +  6  HNO3— v 3  Cu(NO3)2  +  6  H 
and  6  H  +  2  HNO3— ^4  H2O  +  2  NO 

The  sum  of  these  latter  equations  is  the  equation  usually 
written  for  the  reaction  between  copper  and  cold,  dilute 
nitric  acid : 

3  Cu  +  8  HNO3  — >-  3  Cu(NO3)2 .+  4  H2O  +  2  NO 

The  balancing  of  such  an  equation  as  this,  involving 
oxidation  and  reduction,  is  a  somewhat  difficult  matter. 
It  will  probably  be  found  convenient  to  remember  the 
numbers  3  and  8  in  this  reaction. 

When  concentrated  nitric  acid  reacts  with  copper,  nitro- 
gen peroxide  is  formed  in  considerable  quantity,  as  well 
as  some  nitric  oxide  : 

Cu  +  4  HNO3  — >-  Cu(NO3)2  4-  2  NO2  +  2  H2O 

When  very  dilute  nitric  acid  reacts  with  zinc,  or  metals 
similar  to  it,  the  nitrogen  of  the  acid  is  reduced  to  am- 
monia, which  then  combines  with  more  of  the  acid,  forming 
ammonium  nitrate : 

4  Zn  + 10  HN03  — >-  4  Zn(NO3)2  +  NH4NO3  +  3  H2O 

258.  Uses.  —  Nitric  acid  dissolves  silver,  but  does  not 
act  on  gold ;  hence  it  is  sometimes  used  to  separate  these 
two  metals.  The  chief  uses  of  nitric  acid  depend  upon 
its  ability  to. form  unstable  salts  with  organic  bases  (com- 
pounds containing  hydrogen  and  carbon).  Two  of  these 
products  are  nitroglycerine  and  guncotton.  Celluloid  is 
a  mixture  of  nitrocelluloses  and  camphor. 

Aqua  regia  is  a  mixture  of  nitric  and  hydrochloric  acids. 


SODIUM  AND  POTASSIUM  NITRATES  249 

It  dissolves  gold  and  platinum.  The  fact  that  the  mixture 
of  the  acids  does  what  neither  acting  alone  can  do,  is  ex- 
plained by  the  liberation  of  nascent  chlorine  by  the  inter- 
action of  the  two  acids.  The  hydrogen  of  the  hydrochloric 
acid  is  oxidized  by  the  nitric  acid : 

3  HC1  +  HNO3— *-3  Cl  +  2  H2O  +  NO 

Nitric  acid  is  also  extensively  used  in  the  manufacture 
of  many  dyes  and  drugs. 

NITRATES 

259.  Sodium  and  Potassium  Nitrates.  —  The  salts  formed 
by  the  replacement  of  the  hydrogen  of  nitric  acid  are 
called  nitrates.  The  nitrates  of  sodium  and  potassium 
are  the  only  ones  found  in  nature  in  any  considerable 
quantity.  Potassium  nitrate,  ordinary  saltpeter,  is  manu- 
factured in  a  manner  analogous  to  that  by  which  it  is  pro- 
duced in  nature.  In  the  presence  of  bases,  nitrogenous 
organic  matter  decomposes  under  the  influence  of  certain 
minute  organisms  called  nitrifying  bacteria,  and  has  its 
nitrogen  transformed  into  nitrates. 

Sodium  nitrate  is  found  in  large  quantities  in  Chile, 
from  which  fact  it  gets  the  name  Chile  saltpeter.  Nitric 
acid  is  made  from  it.  Because  of  its  great  abundance, 
sodium  nitrate  is  cheaper  than  potassium  nitrate.  The 
following  reaction  will  take  place  in  hot  concentrated 
solution : 

NaNO3  +  KC1  — -+•  KNO3  +  NaCl 

Advantage  is  taken  of  the  fact  to  prepare  the  more  expen- 
sive potassium  nitrate  (§  185). 

One  of  the  chief  uses  of  potassium  nitrate  is  for  the 
manufacture  of  gunpowder.  It  is  also  used  as  a  pre- 
servative in  the  making  of  corned  beef. 


250  NITROGEN  COMPOUNDS 

260.  Calcium  nitrate  has  become  of  importance  on  ac- 
count of  its  production  by  the  reaction  between  a  solution  of 
calcium  hydroxide  and  nitrogen  peroxide  produced  from 
the  atmosphere  by  the  use  of  electricity.     Its  chief  use  is 
in  supplying  combined  nitrogen  to  the  soil  for  plant  food. 

261.  Preparation  of  Nitrates.  — Nitrates,  like  the  salts  of 
the  other  common  acids,  can  be  made  in  several  simple 
ways  in  the  laboratory  : 

(a)  By  the  action  of  nitric  acid  on  metals : 

3  Ag  +  4  HNO3— ^3  AgNO3  +  NO  +  2  H2O 

As  has  been  pointed  out,  hydrogen  is  seldom  a  product  in 
the  action  of  nitric  acid  on  metals. 

(6)  By  the  action  of  nitric  acid  on  oxides  or  hydroxides 
of  metals : 

ZnO  +  2  HNO3 — >•  H2O  +  Zn(NO3)2 

Zn(OH)2  +  2  HN03  — >-2  H2O  +  Zn(NO3)2 

(c)  By  the  action  of  nitric  acid  on  salts  that  give  a 
volatile  product  with  this  acid : 

ZnCO3  +  2  HNO3  — >-  CO2  +  H2O  +  Zn(NO3)2 

Nitrates  cannot  be  prepared  by  precipitation,  because 
nitrates  of  all  metals  are  soluble  in  water.  This  fact  also 
prevents  the  use  of  a  precipitation  method  as  a  test  for  a 
nitrate. 

262.  Test  for  Nitrates.  —  The  test  for  the  NOg-  ion  de- 
pends upon  the  oxidizing  power  of  the  NO8  group.     The 
substance  to  be  tested  is  mixed  with  a  solution  of  ferrous 
sulphate.     Concentrated  sulphuric  acid  is  then  added,  so 
as  to  form  a  layer  below  the  mixed  solution.     Nitric  acid, 
in  the  presence  of  sulphuric  acid,  oxidizes  ferrous  sulphate 


FIXATION  OF  NITROGEN 


251 


to  ferric  sulphate  and,  at  the  same  time,  nitric  oxide,  NO, 
is  formed  as  a  reduction  product.  This  combines  with 
some  of  the  unchanged  ferrous  sulphate  (Fig.  72,  a),  pro- 
ducing a  characteristic  unstable  compound  (whose  formula 
maybe  2  FeSO4.NO), 
which  appears  as  a  dark 
coloration  or  ring  (6) 
just  above  the  heavier 
sulphuric  acid  (e). 

All  nitrates  are  de- 
composed by  heat.  The 
sodium  and  potassium 
salts,  when  thus  treated, 

give  up  oxygen  and  are  converted  into  nitrites.  Other 
nitrates  yield  oxygen  and  nitrogen  peroxide,  and  the  oxide 
of  a  metal. 

263.  Fixation  of  Nitrogen.  —  Nitrogen  compounds  are 
invariably  found  in  certain  tissues  of  both  plants  and 
animals.  The  nitrogen  which  helps  to  form  these  com- 
pounds comes  from  the  soil,  since  neither  plants  nor 
animals,  with  one  exception  about  to  be  noted,  can  take 
nitrogen  from  the  air.  The  problem  how  to  maintain  the 
supply  of  nitrogen  compounds  in  the  soil  was  somewhat 
difficult  to  solve.  The  natural  renewal  of  nitrates  takes 
place  slowly,  and  the  soils  become  infertile  because  of  the 
lack  of  nitrogen  compounds.  This  difficulty  is  usually 
overcome  by  manuring  the  fields,  in  which  case  the  decom- 
posing animal  matter  gives  up  its  combined  nitrogen  to 
the  soil  and  so  to  growing  plants.  Enormous  quantities 
of  nitrogenous  farm  products  are  consumed  in  cities,  and 
most  of  the  combined  nitrogen  contained-  in  these  is  not 
returned  to  the  soil. 

Certain    parasitic    plants    of    microscopic    size,    called 


252 


NITROGEN  COMPOUNDS 


nitrogen-fixing  bacteria,  found  in  the  tubercles  on  the 
roots  of  leguminous  plants,  such  as  peas  and  clover  (Fig. 
73),  have  the  power  of  taking  nitrogen  from  the  air 
and  making  it  available  to  the  plants.  The  nitrogen- 
fixing  bacteria  are  of  great 
importance  in  rendering 
productive  soils  that  had 
remained  infertile  from  the 
lack  of  nitrogen  com- 
pounds. The  process  of 
converting  nitrogen  from 
the  air  into  useful  com- 
pounds is  called  the  fixation 
of  nitrogen.  It  is  difficult 
to  accomplish  because  of 
the  inactive  character  of 
nitrogen.  The  fixation  of 
nitrogen  is  brought  about 
in  nature  to  a  small  extent 
by  the  passage  of  lightning 
through  air.  The  oxygen 
and  nitrogen  unite,  forming 
nitrogen  peroxide,  which  in 
turn  forms  nitric  acid  on 
dissolving  in  water.  Dur- 
ing a  thunderstorm  a  certain  amount  of  nitric  acid  is 
formed  in  this  way. 

The  use  of  atmospheric  nitrogen  in  the  manufacture  of 
ammonia,  calcium  cyanamid,  and  nitric  acid  has  already 
been  briefly  described  (§§  229,  241,  253).  These  pro- 
cesses for  the  fixation  of  nitrogen  are  of  great  importance 
as  a  source  of  nitrogen  for  plant  life. 

Calcium  cyanamid  when  added  to  the  soil  is  soon  con- 
verted into  compounds  that  are  soluble,  and  can  be  ab- 


Copyright  by  The  Scientific  American. 

FIG.   73. — BEAN    ROOTS   SHOWING 
NODULES. 


EXPLOSIVES 


253 


sorbed  by  the  roots  of  plants. 
Ammonium  compounds  and 
nitrates  are  directly  available 
as  plant  food. 

264.  Explosives. — Certain 
nitrogen  compounds  that  con- 
tain carbon,  oxygen,  and  hy- 
drogen are  so  unstable  that 
they  decompose  under  the  im- 
pulse of  a  slight  shock,  forming 
gaseous  products.  For  this 
reason  these  compounds  are 
powerful  explosives.  Nitro- 
glycerine and  guncotton  are 
examples  of  this  class  of  com- 
pounds. Nitroglycerine  is 
made  by  treating  glycerine,  an 
organic  base,  with  a  mixture 
of  nitric  and  sulphuric  acids. 
The  sulphuric  acid  serves  to 
absorb  the  water  that  is  formed 
by  the  reaction  of  the  other 
two  substances : 

C3H6(OH)3  +  3  HN03  — »- 

3H20  +  C3H5(N03)3 

The  nitroglycerine  molecule  is 
evidently  a  very  unstable  one 
that  can  rearrange  itself  into 
new  and  more  stable  molecules 
under  the  impulse  of  a  slight 
shock.  Dynamite  is  a  mixture 
of  wood  pulp,  sodium  nitrate, 


FIG.  74. 


254  NITROGEN  COMPOUNDS 

and  nitroglycerine.  Other  inert  material  may  be  used 
in  place  of  wood  pulp. 

Guncotton  (nitrocellulose)  is  made  by  treating  cotton 
fiber  (cellulose)  with  a  mixture  of  nitric  and  sulphuric 
acids.  Cellulose,  like  glycerine,  is  an  organic  base,  and 
nitrocellulose  is  an  unstable  salt.  Smokeless  powder  is  a 
mixture  of  guncotton  and  nitroglycerine,  or  similar  sub- 
stances. 

Some  forms  of  explosives  containing  nitrogen  com- 
pounds are  shown  in  Fig.  74  :  a  is  granular  gunpowder ; 
6,  cordite ;  <?,  giant  powder ;  d,  brown  prismatic  powder ; 
0,  maximite. 

SUMMARY 

Ammonia  is  formed  in  nature  as  a  decomposition  product  from 
protoplasm. 

It  is  obtained  commercially  as  a  by-product  from  the  distillation 
of  coal.  It  may  be  produced  by  the  action  of  a  base  on  an 
ammonium  salt. 

Ammonia  is  a  gas  with  a  pungent  odor  ;  its  specific  gravity,  rela- 
tive to  hydrogen,  is  8.5.  It  is  very  soluble  in  water,  1  liter  of  water 
at  1 5°  dissolves  720  liters  of  ammonia. 

The  solution  is  basic  and  contains  NH4+  and  OH~  ions.  It 
reacts  with  acids  with  the  formation  of  water  and  an  ammonium 
salt. 

Ammonia  is  used  as  a  refrigerating  agent,  and  in  the  preparation 
of  sodium  bicarbonate  and  of  ammonia  water. 

Nitrogen  forms  five  oxides. 

Nitrous  oxide,  N20,  is  made  by  heating  ammonium  nitrate.  It 
is  a  good  supporter  of  combustion,  and  is  used  as  an  anesthetic 
("  laughing  gas  "). 

Nitric  oxide,  NO,  is  formed  by  the  action  of  dilute  nitric  acid  on 
metals.  It  unites  with  oxygen  at  ordinary  temperatures,  forming 


SUMMARY  255 

nitrogen  peroxide,  N02.     This  is  a  brown,  poisonous  gas,  soluble  in 
water. 

Nitrous  anhydride,  N203,  and  nitric  anhydride,  N2O5,  are  unim- 
portant. 

Nitric  acid  is  prepared  by  the  reaction  between  sulphuric  acid  and 
a  nitrate. 

When  pure,  it  is  a  colorless  liquid,  with  a  specific  gravity  of  1.53. 

It  is  a  powerful  oxidizing  agent,  and  when  it  reacts  with  metals, 
the  hydrogen  is  oxidized  to  water  and  reduction  products  are  formed. 
A  mixture  of  nitric  and  hydrochloric  acid  is  aqua  regia;  this  fur- 
nishes nascent  chlorine. 

Nitric  acid  is  used  in  the  preparation  of  nitrates  and  explosives. 

The  nitrates  of  sodium  and  potassium  are  the  most  important. 
Nitrates  may  be  prepared  by  the  action  of  nitric  acid  on : 

(1)  metals  ;  (2)  oxides  or  hydroxides  ;  (3)  salts  yielding  volatile 
products. 

Potassium  nitrate  is  used  in  gunpowder  and  as  a  meat  preserva- 
tive ;  sodium  nitrate  as  a  fertilizer  and  for  the  production  of 
nitric  acid  and  potassium  nitrate. 

Fixation  of  nitrogen  is  the  conversion  of  the  free  nitrogen  of  the 
atmosphere  into  useful  compounds. 

It  is  brought  about  by  chemical  methods  and  by  the  use  of 
nitrogen-fixing  bacteria.  These  are  processes  that  are  of  great 
importance  in  furnishing  nitrogen  to  plants. 

Nitrifying  bacteria  convert  organic  nitrogen  compounds  into 
ammonia,  nitrites,  and  nitrates. 

Many  nitrogen  compounds  are  used  in  explosives.  Nitro- 
glycerine and  guncotton  are  made  by  the  action  of  nitric  acid  on 
glycerine  and  cotton  respectively.  Dynamite  is  a  mixture  of  inert 
materials  with  nitroglycerine. 


256  NITROGEN  COMPOUNDS 

EXERCISES 

1.  How  many  liters  of  ammonia  can  be  obtained  by  the 
action  of  lime  on  50  grams  of  ammonium  chloride  ? 

2.  Why  is  ammonia  called  the  volatile  alkali  ? 

3.  What  method  would  you  use  to  get  a  few  cubic  centi- 
meters of  ammonia  gas  for  use  in  the  laboratory  ? 

4.  Explain  what  is  meant  by  the  ammonium  theory. 

5.  Show  how  the  nitrogen  oxides  illustrate  the  law  of  mul- 
tiple proportions. 

6.  By  what  tests  would  you  distinguish  between  oxygen  and 
nitrous  oxide  ? 

7.  What  volume  of  air  would  convert  100  c.c.  of  nitric  oxide, 
NO,  into  nitrogen  peroxide,  N02  ? 

8.  Compare  nitric  acid  with  sulphuric  acid  and  with  hydro- 
chloric acid  in  regard  to  its  action  with  metals. 

9.  Tell  about  the  natural  formation  of  (a)  ammonia,  (6)  nitric 
acid,  (c)  nitrates. 

10.  Why  is  nitric  acid  a  better  solvent  than  hydrochloric 
acid  for  silver,  mercury,  and  lead  ? 

11.  What  is  aquafortis  ?  aqua  regia  9  sal  ammoniac  ? 

12.  Upon  what  properties  of  nitric  acid  do  most  of  its  uses 
depend  ?     Illustrate. 

13.  How  would  you  test  an  unknown   substance   for  the 
nitrate  ion  ?     For  the  ammonium  ion  ? 

14.  Explain   the   significance   of  the   statement,   "No  life 
without  nitrogen." 

15.  State  the  substances  and  conditions  necessary  to  yield 
each   of  the   following   products   from   nitrogen   compounds: 
oxygen,  hydrogen,  nitric  oxide,  nitrogen  peroxide. 

16.  Why  has  it  become  necessary  to  devote  much  attention 
to  the  artificial  production  of  fertilizers  containing  nitrogen  ? 

17.  Describe  a  process  for  the  fixation  of  nitrogen. 


CHAPTER   XXIII 
ELEMENTS  OF  THE  NITROGEN  GROUP 

265.  General  Characteristics.  —  The  elements  in  this  group 
resemble  each  other  in  properties  to  a  considerable  degree. 
It  is  approximately  true  that  in  going  through  the  group 
a  given  property  changes  steadily  in  one  direction  as  the 
atomic  weights  increase.  Thus  nitrogen  is  a  colorless 
gas  ;  phosphorus  is  a  waxlike  solid  ;  arsenic  is  a  dark 
gray  solid  with  something  of  the  appearance  of  a  metal ; 
antimony  has  a  distinctly  metallic  appearance  ;  bismuth 
is  a  metal.  Their  respective  specific  gravities  are  :  0.97,1 
1.8,  5.7,  6.7,  9.7.  There  is  a  similar  gradation  of  chemi- 
cal properties  from  the  non-metallic  or  acid-forming  nitro- 
gen and  phosphorus,  through  the  acid-forming  but  faintly 
metallic  arsenic,  to  the  metallic  antimony  and  bismuth, 
which  have  but  faint  traces  of  acid  character. 

The  elements  of  the  family  form  many  compounds 
similar  in  character  and  formula.  All  except  bismuth 
form  compounds  of  the  type  XH3,  where  X  stands  for  the 
symbol  of  any  element  in  the  family.  There  are  two 
oxides,  X2O3  and  X2O5,  which  are  the  anhydrides  of  the 
acids  HXO2  and  HXO3  respectively.  In  the  cases  of 
phosphorus,  arsenic,  and  antimony,  the  acid  formulas  are 
H3XO3  and  H3XO4,  showing  the  addition  of  three  mole- 
cules of  water  to  the  anhydride  instead  of  one. 

X205+H20— -^2  HXO8 
X2O5  +  3  H2O— ^2  H3XO4 

1  Air  =  1 ;  the  other  specific  gravities  refer  to  water. 
257 


258         ELEMENTS   OF  THE  NITROGEN  GROUP 


PHOSPHORUS 

266.  Occurrence.  —  About  one  fourth  of  the  bones  and 
teeth  of  animals  is  calcium  phosphate.  Rock  phosphates, 
containing  calcium  phosphate,  Ca3(PO4)2,  derived  from 
the  bones  of  prehistoric  animals,  are  the  chief  source  of 
phosphorus.  Complex  phosphorus  compounds  are  a  small 
but  very  essential  constituent  of  the  muscles,  nerves,  and 
brains  of  animals.  Soluble  phosphates  are  very  neces- 
sary for  plant  growth,  and  all  vegetable  foods  contain  a 
small  per  cent  of  phosphorus.  Man  derives  his  largest 
supply  from  such  protein  foods  as  beans,  peas,  cheese,  oat- 
meal, meat,  and  bread. 

Phosphorus    was    discovered    in    1669    by    Brand,    an 

alchemist  of  Hamburg, 
while  distilling  urine 
in  the  course  of  his  at- 
tempts to  find  the  phi- 
losopher's stone. 
Scheele,  the  Swedish 
chemist,  prepared  it 
from  bones  in  1771. 


267.  Preparation. — 

Phosphorus  is  obtained 
by  passing  an  electric 
current  through  a  mix- 
ture of  rock  phosphates, 
sand  (SiO2),  and  coke, 


FIG.  75.  —  ELECTRIC  FURNACE   FOR  PHOS- 
PHORUS EXTRACTION. 


or  anthracite  coal.  The  finely  ground  materials  are  put 
in  the  hopper  of  the  electric  furnace  (Fig.  75),  and  then 
drop  upon  the  worm  conveyor  which  feeds  to  the  interior 
of  the  furnace.  The  resistance  of  the  mixture  to  the 
passage  of  the  current  between  the  carbon  electrodes 


WHITE  PHOSPHORUS  259 

develops  intense  heat  which  brings  about  the  following 
reaction  : 

Ca3(P04)2  +  3  Si02  +  50—^3  CaSiO3  +  5  CO  +  2  P 

The  calcium  silicate  forms  a  slag  which  collects  at  the 
bottom  of  the  furnace,  where  it  is  tapped  off  from  time  to 
time.  The  mixture  of  carbon  monoxide  and  phosphorus 
vapors  passes  out  to  the  condenser,  where  the  phosphorus 
is  condensed  by  water,  and  is  run  into  cylindrical  molds. 

268.  White  Phosphorus.  —  Phosphorus  exists  in  two  well- 
known  allotropic  forms  —  the  white  and  the  red. 

White  phosphorus  is  a  waxy,  translucent  solid  which  is 
a  little  less  than  twice  as  heavy  as  water.  It  melts  easily 
(44°  C.),  but  on  account  of  its  inflammability,  the  melting 
must  be  done  under  water.  It  is  readily  soluble  in  carbon 
disulphide.  When  this  solution  is  made  to  evaporate 
slowly,  with  the  exclusion  of  air,  fine  and  almost  colorless 
crystals  of  phosphorus  are  obtained. 

White  phosphorus  is  a  spontaneously  inflammable  sub- 
stance. It  oxidizes  slowly  in  air,  and  the  heat  produced 
raises  the  temperature  of  the  phosphorus  to  its  kindling 
point  (35°  C.).  For  this  reason,  the  phosphorus  is  kept 
under  water.  Phosphorus  burns  in  oxygen  with  a  bril- 
liant flame,  producing  dense  white  fumes  of  phosphorus 
pentoxide  (Fig.  10). 

4  P  +  5  02  — *-  2  P306 

White  phosphorus  when  oxidizing  slowly  glows  in  the 
dark  and  some  ozone  is  produced.  The  odor  of  the  latter 
substance  (or  possibly  that  of  an  oxide  of  phosphorus) 
has  led  to  the  common  error  that  white  phosphorus  has 
an  odor. 

White  phosphorus  is  so  active  that  it  combines  readily 


260         ELEMENTS   OF  THE  NITROGEN  GROUP 

in  the  cold  with  halogens,  and  at  a  moderate  heat  with 
sulphur  and  the  more  energetic  metallic  elements. 

269.  Red  Phosphorus.  —  When  white  phosphorus  is  heated 
to  about  250°  C.  in  a  vessel  from  which  air  is  excluded, 
red  phosphorus  is  obtained.     Light  brings  about  this  con- 
version at  ordinary  temperatures.     This  accounts  for  the 
change  of  color  when  white  phosphorus  is  exposed  to  light. 
After  a  time  a  reddish  coating  may  be  observed.     The 
change   takes  place   more  rapidly  in  a  confined  carbon 
disulphide  solution  exposed  to  light. 

The  change  from  white  to  red  phosphorus  results  in  the 
liberation  of  considerable  heat.  This  indicates  that  red 
phosphorus  is  the  more  stable  at  ordinary  temperatures, 
but  is  less  active.  'Hence  red  phosphorus  is  less  easily 
ignited  and  when  burned  evolves  less  heat  than  an  equal 
weight  of  the  white  variety.  In  general,  red  phosphorus 
reacts  less  readily  than  the  white  form. 

Red  phosphorus  is  a  soft,  reddish  powder  which  is 
slightly  more  than  twice  as  heavy  as  water.  It  is  in- 
soluble not  only  in  water,  but  also  in  carbon  disulphide. 

When  red  phosphorus  is  heated  to  about  290°,  and  the 
resulting  vapors  are  suddenly  cooled,  the  conversion  of 
red  to  white  phosphorus  occurs.  Thus  we  see  that  red 
and  white  phosphorus  are  allotropic  forms  comparable  to 
those  of  sulphur.  The  red  form  is  the  stable  form  at  all 
temperatures  at  which  both  forms  are  known,  and  contains 
less  energy  than  the  white  variety.  In  other  words,  add- 
ing more,  energy  to  the  red  form  converts  it  into  the 
white  variety. 

270.  Phosphorus  Poisoning.  —  Red     phosphorus    is    not 
poisonous,  while    white  phosphorus   is  so  active  a  poison 
that  a  minute  quantity   taken   internally   causes   death. 


MATCHES  261 

Formerly  in  the  making  of  matches,  the  workmen,  by  in- 
haling the  phosphorus  vapors,  contracted  a  painful  disease 
characterized  by  ulceration  of  the  jawbones.  Recently, 
however,  legislation  in  this  country  (as  is  the  case  in 
practically  all  civilized  nations  of  the  world)  has  pro- 
hibited the  use  of  poisonous  white  phosphorus  in  the  manu- 
facture of  matches,  and  instead  red  phosphorus  or  a 
non-poisonous  compound  of  phosphorus,  known  as  phos- 
phorus "  sesquisulphide  "  (P4S3),  is  used. 

The  easily  inflammable  white  phosphorus  should  never 
be  handled  except  with  tongs.  Phosphorus  burns  are 
deep  seated  and  very  difficult  to  heal,  even  if  suppuration 
does  not  occur.  An  alcohol  solution  of  picric  acid  is 
effective  in  their  treatment. 

271.  Uses.  —  Phosphorus  is  used  in  the  manufacture  of 
matches.     Phosphor  bronze  contains  from  0.2%  to  4  %  of 
phosphorus,  either  in  the  form  of  the  phosphide  of  copper 
or  of  the  phosphide  of  tin.     It  is  a  hard,  tenacious  alloy 
which  is  not  corroded  by  water.     A  minor  use  of  phos- 
phorus is  as  a  constituent  of  poisonous  pastes  for  rats  and 
mice. 

272.  Matches.  —  A  common  friction  match  (Fig.  76)  con- 
sists of  a  stick  of  soft  wood,  about  half  an  inch  of  which  has 
been  dipped  in  melted  par- 

affin,  sulphur,  or  other  eas- 
ily ignitible  material;  and  a 
"head"  composed  of  a  mix- 
ture of  an  oxidizing  material  (such  as  potassium  chlorate 
or  oxide  of  lead)  phosphorus,  some  inert  substance  to  in- 
crease the  friction  (such  as  ground  glass  or  flint),  and 
glue  mixed  with  some  coloring  matter.  The  stick  is 
dipped  by  a  machine  into  the  melted  paraffin,  which 


EFLY  LOW  KINDLING  MATERIM. 

FIG.  76.  —  CROSS  SECTION  OF  A  MATCH. 


262         ELEMENTS   OF   THE  NITROGEN  GROUP 

soaks  into  the  wood.  It  is  next  dipped  by  the  same 
machine  into  a  paste  composing  the  "  head,"  and  is  then 
dried.  The  glue  serves  to  bind  the  materials  together 
and  also  protects  the  phosphorus  from  the  action  of  the 
air.  On  rubbing,  sufficient  heat  is  generated  to  ignite  the 
phosphorus  in  contact  with  the  oxidizing  substance.  The 
heat  of  this  combustion  is  sufficient  to  ignite  the  paraffin, 
and  the  burning  of  this  will  in  turn  bring  the  wood  to  its 
kindling  temperature. 

As  friction  matches  are  always  a  source  of  fire  hazard, 
they  are  often  prohibited  and  are  replaced  by  safety 
matches,  the  heads  of  which  consist  of  antimony  tri- 
sulphide,  some  oxidizing  agent,  such  as  potassium  chlorate 
or  dichromate,  and  a  little  powdered  glass  to  increase  the 
friction,  all  held  together  with  glue.  The  box  against 
which  they  are  rubbed  has  a  surface  of  a  thin  layer  of  red 
phosphorus  mixed  with  antimony  trisulphide,  manganese 
dioxide  and  glue.  Sometimes  dextrin  replaces  the  glue. 
As  the  head  of  the  safety  match  is  soft,  it  will  rub  off  on 
a  rough  surface  and  not  burn,  but  it  will  usually  ignite  on 
a  hard,  smooth  surface  that  is  a  poor  conductor  of  heat, 
like  glass  or  slate  blackboard. 

To  prevent  the  smoldering  of  glowing  matches,  the 
sticks  are  sometimes  treated  with  a  fireproofing  material, 
such  as  a  solution  of  sodium  phosphate  or  alum.  The  stick 
is  then  said  to  be  "  impregnated "  and  is  no  longer  a 
source  of  danger  when  thrown  into  waste  by  some  careless 
person. 

273.  Compounds.  —  Phosphorus,  like  nitrogen,  forms  sev- 
eral oxides  and  acids.  Phosphoric  oxide,  P2O5,  is  formed 
when  phosphorus  burns  in  a  sufficient  supply  of  air  or 
oxygen.  It  is  a  white  solid,  which  combines  energetically 
with  water,  forming  phosphoric  acid,  H3PO4. 


ARSENIC  263 

Phosphorus  oxide,  P2Og,  forms  when  phosphorus  burns 
with  a  limited  supply  of  oxygen.  This  white  solid  com- 
bines with  water,  forming  phosphorous  acid,  H3PO3. 

Phosphoric  acid,  H3PO4,  has  several  salts  of  common 
occurrence  :  ordinary  sodium  phosphate,  Na^HPO^  used 
in  medicine;  calcium  phosphate,  Ca3(PO4)2,  the  principal 
mineral  constituent  of  the  bones  ;  monocalcium  acid  phos- 
phate, CaH4(PO4)2,  used  in  baking  powder  and  fertilizers. 

ARSENIC 

274.  Arsenic  is  generally  found  in  nature  combined 
with  sulphur,  associated  with  iron  and  copper.  The  ore 
is  roasted,  forming  arsenious  oxide,  which  is  then  reduced 
with  carbon  : 

30—^2  As  +  SCO 


275.  Properties.  —  Arsenic  is  a  brittle,  steel-gray,  crystal- 
line solid,  with  a  metallic  luster,  and  tarnishes  rapidly  in 
the  air.     It  volatilizes  without  melting  at  the  ordinary 
atmospheric  pressure  and  has  an  odor  like  garlic.    It  burns 
with  a  bluish  flame,  forming  the  oxide,  As2O3.    In  its  physi- 
cal properties,  arsenic  resembles  the  metals,  but  in  its  ac- 
tions, it  resembles  the  non-metals,  especially  phosphorus. 

276.  Uses.  —  Arsenic  is  added  to  lead  in  the  manufacture 
of  shot.     The  melted  alloy  of  lead  and  arsenic  is  dropped 
from  a  height  through  a  strainer  or  collander  into  water. 
The  arsenic  lowers-  the  melting  point  of   the  lead  and 
makes  it  more  fluid,  so  that  the  shot  becomes  spherical 
before  cooling.     The  arsenic  also  makes  the  shot  harder 
than  pure  lead. 

277.  Compounds.  —  Arsenious    oxide,    "white    arsenic," 
As2O3,  is  a  crystalline  powder,  slightly  soluble  in  water, 


264         ELEMENTS   OF  THE  NITROGEN  GROUP 

and,  like  all  compounds  of  arsenic,  is  poisonous.  It  is  used 
in  the  manufacture  of  certain  colors,  also  in  medicine, 
and  as  a  poison.  Sulphides  of  arsenic,  realgar,  As2S2,  and 
orpiment,  As2S3,  are  used  as  pigments.  Paris  green  is  a 
copper  and  arsenic  compound  used  as  pigment  and  as 
insecticide. 

ANTIMONY 

278.  Antimony  is  found  combined  with  sulphur.     It  is 
prepared  in  a  manner  analogous  to  that  for  arsenic,  or  by 
heating  the  sulphide  with  iron: 

Sb2S3  +  3  Fe — ^2  Sb  +  3  FeS 

279.  Properties  and  Uses.  —  Antimony    is    a    brilliant, 
silver-white,  crystalline,  brittle  solid,  with  a  pronounced 
metallic  luster.      It   does  not  tarnish  in  air,  but    when 
heated  in  the  air,  burns,  forming  the  oxide,  Sb2O3.     As  it 
does  not  change  in  air,  it  is  used  to  cover  other  mate- 
rials, such  as  brass  and  lead  alloys.     When  finely  pow- 
dered, it  is  called  antimony  black,  and  is  used  to  coat  plaster 
casts  in  imitation  of  metal.     Antimony  alloys  are  usually 
hard.     Britannia  metal  and  pewter  contain   copper,  tin, 
lead,  and  antimony.     Babbitt  metal  and  other  anti-friction 
alloys  for  bearings  generally  contain  antimony. 

Lead  contracts  on  solidifying ;  an  alloy  of  antimony, 
lead,  and  tin  expands  on  solidifying,  and  is  hard.  This 
alloy  is  used  for  type  metal. 

BISMUTH 

280.  Properties  and  Uses.  —  Bismuth  resembles  antimony, 
but  is  more  metallic.      It  has  a  red  tinge,  is  brittle,  crys- 
talline, heavy,  and  tarnishes  slowly  in  moist  air. 

Bismuth  alloys  are  remarkable  for  their  low  melting- 
points.  Bismuth  melts  at  270°  C.  Its  two  most  common 


COMPARISON  OF  THE  NITROGEN  GROUP      265 


alloys,  Wood's  metal  and  Rose's  metal,  have  the  following 
composition : 


WOOD'S  MBTAL 

ROSE'S  METAL 

Bismuth 

50.0  % 

48.9  % 

Tin 

12.5  % 

23.6  % 

Cadmium 

12.5  % 

Lead      

25.0  % 

27.5  % 

Melting  points    

65°  C. 

95°  C. 

Such  easily  melted  alloys  are  extensively  used  as  fuses 
in  electric  connections,  in  fire  alarms,  in  safety  plugs  for 
boilers,  and  in  automatic  sprinklers  in  buildings.  When 
the  fusible  plug  of  a  sprinkler  (Fig.  77,  a) 
melts,  the  water  rushes  out  from  the  main 
and  strikes  a  cap  5,  scattering  the  water 
in  all  directions.  A  piece  of  Wood's 
metal  is  sometimes  placed  in  the  gaspipe 
where  it  enters  the  building,  so  that  in 
case  of  fire  the  alloy  will  melt  and  stop 
the  flow  of  gas.  FIG.  77. 

281.   Comparison  of  the  Nitrogen  Group. 


• 

ATOMIC 
WEIGHT 

MELTING 
POINT 

HYDRIDES 

OXIDES 

ACIDS 

Nitrogen 

14 

-214° 

NH3 

NA  NO, 

HN02 

NA 

HN03 

NOg,  N205 

Strong  acids 

Phosphorus 

31 

44° 

PH3 

PA,  PA 

H3P03,  H3P04 

Weak  acids 

Arsenic 

75 

volatile  .  .  . 

AsH3 

As2O3,As2O5 

H3AsO3,H3AsO4 

Antimony 

120 

630° 

SbH3 

Sb2O3,  Sb2O5 

H3SbO4 

Very  weak  acids 

Bismuth 

208 

269° 

Bi203 

Bi(OH)3,  Base 

266         ELEMENTS   OF  THE  NITROGEN  GROUP 

SUMMARY 

Phosphorus  exists  in  allotropic  forms.  The  common  ones  are 
the  white  and  the  red.  White  phosphorus  is  the  more  active,  is 
very  inflammable  and  poisonous,  and  dissolves  in  carbon  disulphide. 

Red  phosphorus  is  not  so  easily  ignited,  is  less  active  chemi- 
cally, and  does  not  dissolve  in  carbon  sulphide. 

Phosphorous  is  extracted  by  the  heat  developed  by  passing  an 
electric  current  through  a  mixture  of  rock  phosphates,  sand,  and 
coke. 

Phosphorus  is  chiefly  used  for  making  matches  and  hard  alloys. 

Arsenic,  though  a  non-metal,  shows  some  of  the  characteristics 
of  metals.  It  alloys  with  other  metals  and  is  used  to  make  shot 
hard.  Some  of  its  compounds  are  valuable  as  pigments. 

Antimony  shows  the  characteristics  of  both  metals  and  non- 
metals.  It  is  a  constituent  of  type  metal  and  other  alloys. 

Bismuth  is  a  metal  used  in  many  alloys.  These  alloys  gener- 
ally have  low  melting  points. 

EXERCISES 

1.  What  is  the   per  cent  of  phosphorus  in  calcium  phos- 
phate of  the  formula,  Ca3(P04)2  ? 

2.  Make  a   sketch   of  the  electric   furnace   for  extracting 
phosphorus.     Label  each  part.     Why  must  air  be  kept  out  ? 

3.  Compare,   in  tabular  form,    white  and   red  phosphorus 
with  respect  to  (a)  solubility  in  water  and  in  carbon  disulphide, 
(b)  melting  points,  (c)  ease  of  ignition,  (d)  chemical  activity, 
(e)  poisonous  nature. 

4.  What  weight  of  oxygen  would  be  consumed  in  combining 
with  0.5  gram  of  phosphorus  ?     What  would  be  the  volume  of 
the  oxygen  at  standard  conditions  ? 

5.  Why  is  white  phosphorus  kept  under  water? 


SUMMARY  267 

6.  What  may  be  produced  during  the  slow  oxidation  of 
white  phosphorus  ? 

7.  What  weight  of  phosphorus  would  be  necessary  to  re- 
move the  oxygen  from  10  liters  of  air  (measured  at  standard 
conditions)  ? 

8.  How  may  red  phosphorus  be  changed  to  white  ?     White 
to  red  ? 

9.  Why  does  white  phosphorus  cause  such  bad  burns? 

10.  State  the  essential  differences  between  a  safety  and  a 
friction  match.     How  does  the  safety  match  justify  its  name  ? 

11.  Write  equations  to  show  that  both  phosphorous  oxide 
and  phosphoric  oxide  are  acid  anhydrides. 

12.  Why  do  matches  ignite  on  being  rubbed  ? 

13.  What  is  (a)  phosphor  bronze?  (6)  white  arsenic?  (c)  type 
metal?  (d)  Wood's  metal  ?  (e)  Eose's  metal  ? 

14.  Describe  the  operation  of  an  automatic  sprinkler. 

15.  Eeduced  to  standard  conditions,  500  c.c.  of  phosphorus 
vapor  weigh  2.79  grams.     From  this  calculate  (a)  the  vapor 
density,  (6)  the  number  of  atoms  in  a  molecule  of  gaseous 
phosphorus. 


CHAPTER   XXIV 

THE   HALOGENS 

THE  elements  fluorine,  chlorine,  bromine,  and  iodine  are 
called  halogens  (salt  formers),  because  they  unite  directly 
with  a  large  number  of  metallic  elements  to  form  salts. 

BROMINE 

282.  Occurrence.  —  Bromine  was  discovered  in  1826  by 
Ballard,  who  separated  it  from  the  mother  liquor  of  sea 
salt,  known  as  bittern  on  account  of  the  bitter  taste  im- 
parted by  magnesium  salts.     Extensive  deposits  of  mag- 
nesium salts  containing  bromides  are  found  in  the  almost 
inexhaustible   salt    beds    at    Stassfurt,    Germany.       The 
United  States  and  Germany  furnish  a  large  percentage 
of  all  the  bromine  used.      Large  deposits  of  crude  salt, 
impure  sodium  chloride,  occur  in  the  states  of  Michigan, 
West  Virginia,  Ohio,  and  Kentucky.      Magnesium  bro- 
mide   and   sodium   bromide   are   two    of  the   substances 
mixed  with  the  sodium  chloride. 

283.  Commercial  Preparation. —  When   the   brines   from 
these  deposits  are  evaporated,  nearly  all  of  the  sodium 
chloride  crystallizes  out  before  the  magnesium  salts  be- 
gin to  separate  in  an  appreciable  quantity.     The  liquid 
remaining  after  a  portion   of  the   substances   contained 
in  the  original  solution  has   crystallized,    is   known  by 
the  technical  name  of  mother  liquor.     The  mother  liquor 
containing  the  magnesium  chloride  is  allowed  to  trickle 


PREPARATION   OF  BROMINE 


269 


down  through  a  tower  filled  with  small  pieces  of  stone 
or  brick.  Chlorine  gas  enters  at  the  bottom  of  the  tower, 
and,  as  it  rises,  reacts  with  the  descending  solution : 

MgBr2  +  C12  — *~  MgCl2  +  Br2 

High  pressure  steam  introduced  into  the  apparatus  causes 
the  liberated  bromine  and  any  excess  of  chlorine  to  pass 
over  at  the  top  of  the  tower.  The  bromine  is  condensed 
in  a  receiver  and  is  afterwards  freed  from  any  chlorine  by 
redistillation. 

284.  Laboratory  Prepara- 
tion. —  Bromine  can  be  pre- 
pared from  the  bromides 
by  a  method  analogous  to 
one  of  the  methods  de- 
scribed for  the  preparation 
of  chlorine ;  namely,  by 
heating  a  mixture  of  a 
bromide,  manganese  di- 
oxide, and  sulphuric  acid 
(Fig.  78).  Bromine,  hav- 
ing a  low  boiling  point, 
passes  off  in  the  state  of 
vapor,  which  can  easily  be 
liquefied  by  keeping  the 
receiver  cool.  If  a  small 
quantity  is  made,  the  bromine  vapor  can  be  condensed 
in  a  test  tube  partly  filled  with  water  (see  a  and  b  in 
Fig.  78). 

The  reaction  may  be  considered  as  taking  place  in  three 
steps. 

Sulphuric  acid  reacts  with  potassium  bromide  to  produce 
potassium  sulphate  and  hydrogen  bromide : 


FIG.  78.  —  PREPARATION  OF  BROMINE. 


270  THE  HALOGENS 

2  KBr  +  H2SO4  — >-  K2SO4  +  2  HBr 

"\yhen  warm  sulphuric  acid  is  added  to  manganese  diox- 
ide, manganese  sulphate,  water,  and  oxygen  are  formed : 

Mn02  +  H2S04  — >-  MnS04  +  H2O  +  O 

Nascent  oxygen  oxidizes  hydrogen  bromide,  forming 
water  and  bromine : 

2HBr  +  O— >-H2O  +  Br2 
The  equation  for  the  complete  reaction  is  : 
2KBr+MnO2  +  2H2SO4— ^K2SO4+MnSO4+2H2O  +  Br2 

285.  Physical  Properties.  — Bromine  is  a  dark  brownish- 
red  liquid,  about  three  times  as  dense  as  water.  It  is  the 
only  non-metallic  element  that  exists  in  the  state  of  a  liquid 
under  ordinary  conditions.  Bromine  has  an  odor  some- 
what resembling  that  of  chlorine  ;  its  name  is  derived  from 
a  Greek  word  meaning  stench. 

When  a  bottle  of  bromine  is  opened,  the  brownish-red 
vapor  of  bromine  can  be  seen  issuing  from  its  mouth.  If 
a  few  drops  of  bromine  are  poured  into  a  large  bottle  filled 
with  air,  the  vapor  is  seen  first  at  the  bottom  of  the  bottle, 
and  from  here  it  diffuses  slowly  until  it  fills  the  bottle. 

The  vapor  of  bromine  has  a  strong  corrosive  action  on 
the  mucous  membrane.  When  it  comes  into  contact  with 
the  eyes,  the  irritation  is  sufficient  to  cause  a  copious  flow 
of  tears.  Great  care  should  be  taken  not  to  inhale  bromine 
vapor,  and  never  to  allow  the  bromine  to  come  in  contact 
with  the  skin.  If  bromine  is  accidentally  inhaled,  the  irri- 
tation can  be  lessened  by  smelling  of  ammonia,  chloroform, 
or  alcohol.  If  bromine  should  come  in  contact  with  the 
skin,  the  injured  part  should  be  washed  freely  with  water 
and  then  covered  with  a  paste  made  by  mixing  sodium  bi- 


PROPERTIES   OF  BROMINE  271 

carbonate  with  water,  or  better,  with  some  oil,  as  olive  or 
cocoanut. 

Bromine  is  somewhat  soluble  in  water ;  the  solution  is 
called  bromine  water.  Bromine  is  more  soluble  in  aqueous 
solutions  of  the  bromides  than  it  is  in  pure  water.  It  is  very 
soluble  in  chloroform  and  in  carbon  disulphide ;  in  both 
solutions  it  has  a  very  characteristic  reddish  yellow  color. 

286.  Chemical  Properties.  —  The   chemical   behavior  of 
bromine  very  closely  resembles  that  of  chlorine.     Bromine 
is,  however,  not  so  active  an  element  as  chlorine.     We 
have  already  seen  that  when  a  mixture  of   chlorine  and 
hydrogen  is  placed  in  the  sunlight,  the  elements  combine 
with  explosive  violence  to  form  hydrogen  chloride.     Un- 
der similar  conditions,  bromine  vapor  and  hydrogen  enter 
into  only  a  partial  combination,  without  any  display  of 
energy.     Aqueous  solutions  of  bromine  bleach  many  dyes, 
but  the  action  is  not  so  rapid  as  in  the  case  of  chlorine. 

Bromine  combines  directly  with  a  number  of  elements,  as 
phosphorus,  antimony,  copper,  and  iron,  forming  bromides. 

287.  Uses.  —  Bromine  is  used  in  the  preparation  of  bro- 
mides and  as  a  mild  oxidizing  agent  in  the  manufacture 
of  many  organic  compounds,  especially  certain  drugs  and 
dyes.     Its  water  solution  is  used  in  the  laboratory  as  an 
oxidizing  agent.     Bromine  is  sometimes  used  as  a  disin- 
fectant, particularly  when  conditions  might  lead  to  an 
epidemic. 

HYDROBROMIC   ACID 

288.  Preparation.  — Hydrogen  bromide  may  be  prepared 
by  the  direct  combination  of  bromine  with  hydrogen ;  the 
method,  however,  is  of  no  practical  importance. 

The  addition  of  sulphuric  acid  to  a  bromide  would  prob- 
ably appear  to  be  a  convenient  method  for  the  preparation 


272  THE  HALOGENS 

of  hydrogen  bromide.  A  dilute  solution  of  hydrobromic 
acid  is  prepared,  on  a  commercial  scale,  by  the  reaction 
between  diluted  sulphuric  acid  and  a  solution  of  potas 
sium  bromide.  The  actual  carrying-out  of  the  process 
requires  considerable  time  and  careful  regulation  of  tem- 
perature. 

When  concentrated  sulphuric  acid  is  added  to  potassium 
bromide,  hydrogen  bromide  appears  as  a  gas,  which  fumes 
as  soon  as  it  comes  in  contact  with  the  air.  Other  gases 
are  formed  at  the  same  time ;  the  odor  of  sulphur  dioxide 
can  generally  be  detected,  and  sometimes  that  of  hydrogen 
sulphide.  The  products  formed  vary  with  the  concentra- 
tion of  the  sulphuric  acid  and  the  temperature  at  which 
the  reaction  takes  place.  The  more  concentrated  the  sul- 
phuric acid,  and  the  higher  the  temperature,  the  less  will 
be  the  amount  of  the  hydrogen  bromide  produced. 

Let  us  consider  the  reactions  involved  when  sulphur 
dioxide  is  formed.  Sulphuric  acid  reacts  with  potassium 
bromide  to  form  potassium  sulphate  and  hydrogen  bro- 
mide : 

2  KBr  +  H2SO4  -^  K2SO4  +  2  HBr 

The  excess  of  concentrated  sulphuric  acid,  however,  oxi- 
dizes part  of  the  hydrogen  bromide,  the  result  of  the  oxida- 
tion being,  water  and  bromine  : 

2  HBr  +  H2S04— ^  2  H2O  +  SO2  +  Br2 

This  is  similar  to  the  action  of  hot,  concentrated  jul- 
phuric  acid  with  copper  (§  220),  in  which  a  portion  of 
the  sulphuric  acid  is  reduced  to  sulphur  dioxide,  and  at 
the  same  time  water  is  formed.  The  fact  that  when 
one  substance  is  oxidized  some  other  substance  is  reduced, 
should  be  constantly  kept  in  mind. 

If  we  use  one  equation  to  represent  the  formation  of 


REPLACEMENT  OF  BROMINE  273 

bromine  and  sulphur  dioxide,  by  the  method  just  consid- 
ered, we  obtain: 

2  KBr  +  2  H2SO4 — ^K2SO4  +  2  H2O  +  SO2  +  Bra 

289.  Properties  and  Uses.  —  Hydrogen  bromide  is  a  color- 
less gas,  readily  soluble  in  water,  and  its  solution,  "hydro- 
bromic  acid,  possesses   the  characteristic  properties  of   a 
strong  acid.     It  is  easily  oxidized  by  the  oxygen  of  the 
air,  water  and  bromine  resulting  from  the  oxidation. 

Dilute  solutions  of  hydrobromic  acid  are  used  to  some 
extent  for  medicine,  and  the  bromides  are  an  important 
series  of  salts. 

290.  Replacement  of  Bromine. — When  chlorine  is  added 
to  a  solution  of  a  bromide,  free  bromine  appears  and  chlo- 
rine molecules  change  into  chlorine  ions.    The  solution  of 
potassium  bromide  contains  potassium  ions,  bromine  ions, 
and   molecules  of   potassium  bromide;  the  undissociated 
and   dissociated   potassium    bromide   are  in  equilibrium. 
As  soon  as  chlorine  is  added,  the  bromine  ions  give  their 
negative  charge  of  electricity  to  the  chlorine  molecules, 
which   then   dissociate    into    ions.       The   bromine    ions, 
having  lost  their  charge  of  electricity,  unite  to  form  bro- 
mine molecules.     As  soon  as  some  of   the  bromine  ions 
pass  out  of  solution,  the  equilibrium  between  the  dissoci- 
ated and  the  undissociated  potassium  bromide  is  destroyed, 
and  more  molecules  of  potassium  bromide  dissociate.     If 
enough  chlorine  is  added,  all  the  bromine  ions  will  finally 
appear  as  bromine  molecules,  and  the  solution  will  contain 
potassium   ions,    chlorine    ions,   molecules    of    potassium 
chloride,  and  molecules  of  bromine : 

2  K+  +  2  Br-  +  C12 — ^-2  K+  +  2  Cl-  +  Bra 
or  2  KBr  +  C12— -^2  KC1  +  Bra 


274 


THE  HALOGENS 


The  presence  of  bromine  can  be  shown  by  adding  a  little 
chloroform  or  carbon  disulphide,  and  shaking.  These 
liquids  and  water  are  not  miscible  (§52),  and  bromine  is 
much  more  soluble  in  carbon  disulphide  than  it  is  in  water. 
The  bromine  will  be  distributed  between  the  water  and  the 
carbon  disulphide  in  proportion  to  its  solubility  in  the  two 
liquids.  The  solution  of  bromine  in  carbon  disulphide  has 
a  characteristic  color;  the  bromine  must  be  free,  for  bro- 
mine ions  do  not  produce  the  characteristic  color,  as  is 
shown  by  shaking  carbon  disulphide  with  a  solution  of 
potassium  bromide  (Fig.  79,  a).  Since  a  small  quantity  of 
carbon  disulphide  can  be  used  to  remove  nearly  all  of  the 
free  bromine  from  a  comparatively  large  quantity  of  water 

by  shaking,  the  process  is  called 
shaking  out  or  extraction. 

291 .   Test  for  a  Bromide.  —  The 

liberation  of  bromine  by  chlo- 
rine, followed  by  shaking  out 
with  chloroform  or  carbon  di- 
sulphide, is  used  as  a  test  for 
bromine  ions.  If  we  add  chlo- 
rine water  to  a  solution  of  a 
bromide,  and  then  shake  with 
chloroform,  the  latter  dissolves 
the  free  bromine,  acquiring  the 
characteristic  reddish  yellow 
coloration  (Fig.  79,  6).  An- 
other test  for  a  bromide  depends 
upon  the  fact  that  silver  bromide  separates  as  a  yellowish 
white  precipitate  when  a  solution  of  silver  nitrate  is  added 
to  a  solution  of  a  bromide.  It  is  insoluble  in  nitric  acid, 
slightly  soluble  in  dilute  ammonium  hydroxide,  and  more 
readily  soluble  in  concentrated  ammonium  hydroxide. 


FIG.  79. 


PHYSICAL  PROPERTIES  OF  IODINE  275 

IODINE 

292.  Discovery — Iodine  was  discovered  by  Courtois  in 
1812    while   trying   to   prepare    potassium    nitrate    from 
liquors  obtained  by  washing  the  ashes  of  burnt  seaweed. 
During  his  experiments  Courtois  observed  the  violet  color 
of  the  vapor  of  iodine,  but  the  properties  of  .the  element 
were  first  carefully  studied  by  Gay-Lussac. 

293.  Preparation.  —  When  seaweed  (kelp)  is  burned  at 
a  low  temperature,  the  ash  contains  considerable  quanti- 
ties of  the  iodides  of  potassium  and  sodium.     As  both  of 
these  salts  are  readily  soluble  in  water,  they  can  be  sepa- 
rated from  the  insoluble  portion  of  the  ash  by  leaching,  that 
is,  by  allowing  water  to  pass  slowly  through  the  ash  and 
dissolve  the  soluble  materials. 

Iodine  is  obtained  from  potassium  iodide  by  a  process 
analogous  to  that  described  for  the  preparation  of  bromine 
(§  284);  the  iodide  is  warmed  with  manganese  dioxide 
and  sulphuric  acid.  Iodine  passes  off  in  the  form  of  a 
vapor : 

2KI  +  MnO2  +  2H2SO4 — ^K2SO4  +  MnSO4  +  2H2O+  I2 

Large  deposits  of  impure  sodium  nitrate  are  found  in  the 
dry  region  west  of  the  Andes.  Compounds  of  iodine  occur 
in  these  deposits,  and  most  of  the  iodine  used  is  obtained 
from  the  mother  liquor  of  the  sodium 
nitrate  works. 


294.   Physical  Properties.  —  Iodine  is  a 
steel-gray  solid  (Fig.  80),  very  slightly 
soluble  in  water,  but  readily  soluble  in    FIG.  80.  — IODINE 
alcohol,  chloroform,  carbon  disulphide, 
and  in  aqueous  solutions  of  potassium  iodide.     A  solution 
of  iodine  in  alcohol  is  called  tincture  of  iodine.    Solutions  of 


276 


THE   HALOGENS 


iodine  in  chloroform  and  in  carbon  disulphide  possess  a 
characteristic  violet  color;  iodine  vapor  has  the  same 
color.  Iodine  vaporizes  slowly  at  ordinary  temperatures. 
When  the  solid  is  warmed,  the  change  takes  place  rapidly, 
and  the  vapor  on  being  cooled  passes  directly  to  the  state  of 
a  solid.  Such  a  distillation  of  a  solid  is  called  sublimation, 
and  may  be  used  to  purify  solids  that  can  be  sublimed,  as 
distillation  is  used  to  purify  liquids. 

The  fact  that  iodine  is  more  soluble  in  a  solution  of  an 
iodide  than  in  pure  water  is  explained  by  the  supposition 
that  iodine  ions  combine  with  the  iodine  molecules  to  form 
triiodine  ions : 

I    4- 12  — >- 1  3 

The  difference  between  the  color  of  a  solution  of  iodine  in 
chloroform  and  the  color  of  a  solution  of  iodine  in  an  aque- 
ous solution  of  an  iodide  is 
due  probably  to  the  differ- 
ence in  the  number  of 
atoms  in  the  particles  of 
iodine  entering  the  solu- 
tion. 

295.   Chemical    Properties. 

—  Iodine  unites  directly 
with  many  elements  to  form 
iodides.  The  reactions  are 
not  as  energetic  , as  in  the 
case  of  either  chlorine  or 
bromine.  When  a  piece  of 
yellow  phosphorus  and  a 
piece  of  iodine  are  brought 
together,  they  combine  to 

form  an  iodide  without  the  application  of  heat  (Fig.  81). 

Iodine  and  iron  unite  when  heated. 


FIG.  81. 


IODIDES  277 

When  a  dilute  solution  of  iodine  is  mixed  with  a  dilute 
solution  of  starch  paste,  a  characteristic  blue  color  is  pro- 
duced. The  reaction  is  employed  in  testing  for  either 
iodine  or  starch. 

296.  Uses.  —  Iodine  compounds  are  used  in  medicine,  in 
photography,  and  for  dyeing.     Tincture  of  iodine  is  used 
for  reducing  swellings  and  as  a  disinfectant  for  wounds. 

297.  Preparation  of  Hydriodic  Acid.  —  If    concentrated 
sulphuric  acid  is  added  to  an  iodide,  the  odor  of  hydrogen 
sulphide  is  very  noticeable.     More  hydrogen  sulphide  is 
produced  than  is  formed  when  sulphuric  acid  is  added  to 
a  bromide.     This  means  that  hydriodic  acid  is  more  easily 
oxidized  (or  is  a  better  reducing  agent)  than  hydrobromic 
acid. 

The  formation  of  iodine  by  the  action  of  sulphuric  acid 
with  potassium  iodide  can  be  represented  by  the  following 
equations  : 

8  KI  +  4  H2SO4  —  >-  4  K2S04  +  8  HI 
H2SO4  +  8  HI  —  ->-  H2S  '+  4  H2O  +  81 

The  equation  for  the  complete  reaction  is: 


8  KI  +  5  H2S04_  -^4  K2S04  +  4  H2O  +  H2S  +  8  I 

Hydriodic  acid  can  be  readily  prepared  by  the  reaction 
of  water  with  iodine  and  red  phosphorus  : 

P    +    31—*-  Pig 

PI8  +  3  H20  —  ^  HgPOg  +  3  HI 

298.  Iodides.  —  The  iodides  are  important  compounds, 
finding  extensive  use  in  medicine. 

Both  chlorine  and  bromine  liberate  iodine  from  the 
iodides  : 


278 


THE  HALOGENS 


2KI  +  C12— -^ 

2  KI  +  2  Br  — >-  2  KBr  +  21 

The  presence  of  free  iodine  can  be  determined  by  the 
starch  test  or  by  shaking  out  with  chloroform  or  carbon 

disulphide. 

THE  HALOGENS   AS   A  GROUP 

299.  Comparison  of  the  Properties  of  the  three  halogens, 
chlorine,  bromine,  and  iodine,  leads  to  some  interesting 
results : 


NAME  OF 
ELEMENT 

ATOMIC 
WEIGHT 

STATE 

SOLUBILITY  IN 
ONE  PART  OP 
WATER  AT 
15°  C. 

HEAT  OP  FORMA- 
TION OP  HYDRO- 
GEN COMP. 

HEAT  OF  FOR- 
MATION OF  PO- 
TASSIUM COMP. 

Chlorine 

35.5 

GaV 

2.4  vol. 

22,000  cal. 

104,300  cal. 

Bromine 

80 

Liquid 

0.032  pt. 

8,400  cal. 

95,100  cal. 

Iodine 

127 

Solid 

0.00015  pt. 

-7,000  cal. 

80,100  cal. 

Chlorine,  bromine,  and  iodine  form  a  natural  group  of 
elements.  The  difference  between  the  atomic  weight  of 
bromine  and  that  of  chlorine  is  nearly  the  same  as  the 
difference  between  the  atomic  weights  of  iodine  and 
bromine.  An  examination  of  the  table  will  show  that  the 
properties  of  these  elements  vary  in  degree  with  the 
atomic  weights.  Chlorine,  bromine,  and  iodine  very 
closely  resemble  each  other  in  their  chemical  behavior. 
The  chemical  activity  of  bromine  is  less  than  that  of 
chlorine  and  greater  than  that  of  iodine. 

300.  Heat  of  Formation.  —  When  a  chemical  change 
occurs  without  the  addition  of  energy,  the  substances 
resulting  from  the  reaction  usually  contain  less  energy 
than  the  original  constituents.  Chemical  energy  has  been 
transformed  into  some  other  kind  of  energy.  It  is  most 
often  liberated  in  the  form  of  heat. 


HEATS   OF  FORMATION  279 

When  elements  unite  to  form  chemical  compounds,  the 
heat  evolved  or  absorbed  is  called  the  heat  of  formation  of 
the  compound  in  question.  In  measuring  the  heat  of 
formation  of  any  compound,  weights  of  the  substances 
equal  to  their  molecular  weights  expressed  in  grams  (gram- 
molecules)  are  considered,  and  the  quantity  of  heat  is 
commonly  expressed  in  calories  (§  48).  The  heat  of 
formation  is  the  number  of  calories  of  heat  absorbed  or 
liberated  during  the  formation  of  one  gram-molecule  of  a 
compound  from  its  elements. 

Hydrogen  unites  with  chlorine  to  form  hydrogen  chlo- 
ride. The  simplest  equation  representing  the  reaction  is: 

H  +  Cl  —  >-  HC1 

This  shows  that  1  gram  of  hydrogen  unites  with  35.5 
grams  of  chlorine  to  form  36.5  grams  of  hydrogen  chlo- 
ride. During  the  combination,  22,000  calories  of  heat 
are  evolved.  The  thermal  equation  for  the  formation  of 
hydrogen  chloride  is: 

H  +  Cl  —  >-  HC1  +  22,000  calories 

The  heat  of  formation  of  hydrogen  chloride  is  22,000 
calories. 

When  hydrogen  combines  with  iodine  to  form  hydrogen 
iodide,  an  absorption  of  heat  occurs.  The  thermal  equa- 
tion reads: 

H  +  I  —  >-  HI  -  7000  calories 


This  shows  that  when  1  gram  of  hydrogen  unites  with  127 
grams  of  iodine,  7000  calories  of  heat  are  absorbed.  The 
heat  of  formation  of  hydrogen  iodide  is  —  7000  calories. 

301.   Relative  Replacement  and  Heats  of  Formation.  —  Let 
us  use  the  double  arrow  in  the  following  equation  to  indi- 


280  THE  HALOGENS 

cate  the  two  possible  directions  in  which  the  reaction  might 
proceed  : 


Would  bromine  actually  replace  chlorine  or  would  the  re- 
verse be  true  ?  The  following  generalization  has  been 
developed  from  the  study  of  the  heat  effects  of  many 
chemical  changes. 

When  a  chemical  reaction  takes  place  without  the  addition 
of  heat  from  an  external  source,  those  substances  which  have 
the  greatest  heat  of  formation  will  tend  to  form. 

The  heat  of  formation  of  hydrogen  bromide  is  8400  cal- 
ories ;  that  of  hydrogen  chloride  is  22,000  calories.  Thus 
more  heat  is  liberated  when  hydrogen  unites  with  chlorine 
than  is  liberated  when  hydrogen  combines  with  bromine. 
We  should  therefore  expect  chlorine  to  liberate  bromine 
from  hydrogen  bromide.  Chlorine  does  liberate  bromine 
from  hydrogen  bromide.  Either  chlorine  or  bromine  lib- 
erates iodine  from  hydrogen  iodide,  as  the  heats  of  for- 
mation of  hydrogen  chloride,  bromide,  and  iodide  would 
lead  us  to  expect.  A  study  of  -the  heats  of  formation  of 
chemical  compounds  has  been  of  value  in  the  prediction  of 
chemical  reactions. 

It  should  be  remembered  that  heat  is  not  the  only  form 
of  energy  into  which  chemical  energy  is  converted,  and  in 
cases  of  solution  in  which  chemical  compounds  are  disso- 
ciated, the  energy  necessary  to  dissociate  the  compounds  is 
an  important  factor  in  the  thermal  equation. 

FLUORINE 

302.  Activity.  —  Fluorine  belongs  to  the  halogen  group, 
but  does  not  so  closely  resemble  the  other  members  of  the 
group  as  they  resemble  each  other.  A  consideration  of 


PREPARATION  OF  FLUORINE 


281 


fluorine  has  therefore  been  made  to  follow  a  study  of  the 
other  members  of  the  group. 

Fluorine  is  an  element  of  unusual  chemical  activity ; 
few  substances  are  not  attacked  by  it.  It  cannot  be 
isolated  in  the  presence  of  water,  as  it  unites  with  the 
hydrogen  in  the  solution  and  liberates  the  oxygen.  Fur- 
thermore, it  cannot  be  prepared  in  glass  vessels,  as  it 
reacts  with  the  glass.  The  heats  of  formation  of  the 
fluorides  are  too  great  to  permit  of  their  being  easily  de- 
composed by  heat.  From  the 
statements  just  made  it  will 
be  seen  that  fluorine  cannot 
be  prepared  by  the  methods 
generally  employed  in  the 
preparation  of  the  other 
halogens. 


303.   Preparation.  —  The 

problem  of  isolating  pure  fluor- 
ine puzzled  chemists  until 
1886,  when  Moissan  discovered 

that  a  solution  of  potassium  fluoride  in  liquid  hydrofluoric 
acid  conducted  the  electric  current.  The  apparatus  used 
fry  Moissan  to  carry  on  the  electrolysis  consisted  of  a  U- 
tube  made  of  an  alloy  of  platinum  and  iridium,  carrying 
electrodes  composed  of  the  same  material,  which  were  in- 
sulated from  the  U-tube  by  calcium  fluoride  stoppers 
(Fig.  82).  Moissan  subsequently  found  that  a  U-tube 
made  of  copper  could  be  substituted  for  the  one  composed 
of  the  expensive  alloy  mentioned. 

The  solution  of  potassium  fluoride  in  hydrofluoric  acid 
was  placed  in  the  U-tube  and  kept  at  a  temperature  near 
—  23°  C,  during  the  electrolysis. 

Fluorine  is  liberated  at  the  anode,  during  the  electrolysis, 


282  THE  HALOGENS 

and  passes  off  through  the  side  arm  of  the  tube  surround- 
ing it.  Hydrogen  is  liberated  at  the  cathode.  Potassium 
passes  to  the  cathode,  but,  on  giving  up  its  electric  charge, 
instantly  unites  with  fluorine,  forming  potassium  fluoride, 
which  dissolves  in  the  excess  of  hydrofluoric  acid.  The 
result  of  this  electrolysis  is  that  only  the  hydrofluoric  acid 
is  permanently  decomposed. 

304.  Properties.  —  At. ordinary  temperatures,  fluorine  is 
a  nearly  colorless  gas,  much  more  poisonous  than  chlorine. 
Liquid  fluorine  combines  energetically  with  hydrogen,  sul- 
phur, phosphorus,  arsenic,  some  other  elements,  and  many 
compounds,  showing  that  violent  chemical  action  can  take 
place  at  a  very  low  temperature. 

Under  ordinary  conditions,  fluorine  has  a  greater  tend- 
ency to  form  compounds  than  any  other  element.  Copper 
when  placed  in  fluorine  becomes  coated  with  an  insoluble 
coating  of  copper  fluoride.  The  fluorides  of  calcium, 
strontium,  and  barium  are  insoluble.  Silver  fluoride  is 
soluble.  Gold  and  platinum,  which  readily  form  com- 
pounds with  nascent  chlorine,  are  very  slowly  attacked  by 
fluorine.  No  oxide  of  fluorine  is  known.  It  is  interest- 
ing to  compare  the  properties  of  fluorine  just  mentioned 
with  those  of  chlorine,  bromine,  and  iodine. 

Two  compounds  of  fluorine  that  occur  in  nature  are  of 
importance:  calcium  fluoride  or  fluor  spar,  CaF2,  and  cryo- 
lite, 3NaF.AlF3.  Cryolite  is  used  in  the  preparation  of 
aluminum  by  the  electrolytic  process. 

305.  Hydrofluoric  Acid.  —  Hydrofluoric  acid  is  prepared 
by  the  action  of  sulphuric  acid  with  fluor  spar : 

CaF2  +  H2S04  — >•  CaS04  +  2  HF 

The  reaction  is  commonly  carried  on  in  a  lead  or  platinum 
dish. 


HYDROFLUORIC  ACID 


283 


Pure  hydrogen  fluoride  is  a  colorless  liquid  which  fumes 
strongly  in  air.  It  dissolves  readily  in  water  and  aque- 
ous solutions  of  it  are  sold  in  wax  bottles.  Great  care 
should  be  exercised  in  using  this  acid,  as  painful  sores, 
difficult  to  heal,  are  produced  when  it  comes  in  contact 
with  the  skin.  There  have  been  cases  where  the  inhalation 
of  hydrogen  fluoride  vapor  has  caused  death. 

The  chief  use  of  hydrofluoric  acid  is  in  the  etching  of 
glass.  Glass  is  composed  of  silicates,  and  hydrofluoric 
acid  converts  the  silica  (silicon  dioxide)  of  the  glass  into 
a  gas,  silicon  fluoride,  and  water : 

SiO2  +  4  HF  — >-  SiF4  +  2  H2O 

Glass  is  prepared  for  etching  by  covering  it  with  a  coat- 
ing of  some  substance  that  is  not  attacked  by  hydro- 
fluoric acid,  such  as 
paraffin  or  a  mixture  of 
beeswax  and  rosin,  and 
then  removing  the  coat- 
ing with  a  sharp  instru- 
ment from  the  part  to 
be  etched.  The  etching 
is  accomplished  by  sub- 
jecting the  prepared 
piece  to  hydrofluoric 
acid  vapor,  or  by  ap- 
plying to  it  a  water  so- 
lution of  the  acid  (Fig.  83).  When  the  gas  is  used  the 
surface  of  the  etching  is  left  dull,  while  with  a  water 
solution  it  is  left  glossy.  Hydrofluoric  acid  is  used  in 
the  finishing  of  cut  glass,  and  for  the  removal  of  sand 
from  castings.  Sodium  and  ammonium  fluoride  solutions 
also  are  used  for  etching  glass. 


FIG. 


83.  —  ETCHING   WITH 
ACID. 


HYDROFLUORIC 


284  THE  HALOGENS 

SUMMARY 

Bromine,  atomic  weight,  80,  resembles  chlorine  very  closely. 
The  chief  points  of  difference  are  that  it  is  a  dark-colored  liquid 
and  that  it  is  less  active.  In  general,  bromine  reactions  resemble 
those  of  chlorine,  but  are  of  less  intensity. 

Bromides  are  found  in  nature  associated  with  chlorides.  Bro- 
mine is  prepared  from  bromides  by  a  process  exactly  analogous  to 
that  used  in  the  preparation  of  chlorine  from  sodium  chloride.  A 
mixture  of  a  bromide  and  manganese  dioxide  is  treated  with  con- 
centrated sulphuric  acid.  The  manganese  dioxide  acts  as  an 
oxidizing  agent  on  the  hydrobromic  acid  that  is  formed  by  the 
action  of  the  sulphuric  acid  with  the  bromide. 

Hydrobromic  acid  is  the  water  solution  of  hydrogen  bromide, 
which  is  formed  by  the  action  of  moderately  concentrated  sulphuric 
acid  with  potassium  bromide.  There  is  a  marked  difference 
here  from  the  action  that  occurs  in  the  preparation  of  hydro- 
chloric acid.  The  difference  is  due  to  the  fact  that  the  hydro- 
bromic acid  is  less  stable  (i.e.  has  a  less  heat  of  formation)  than 
hydrochloric  acid.  The  secondary  products  formed  in  the  case  of 
hydrobromic  acid  are  mainly  sulphur  dioxide  and  free  bromine, 
resulting  from  the  oxidizing  action  of  the  sulphuric  acid. 

Bromine  and  its  compounds  are  not  of  great  commercial  impor- 
tance. Bromides  are  used  in  medicine,  and  free  bromine  is  used 
in  the  preparation  of  certain  dyes. 

Since  bromides  have  smaller  heats  of  formation  than  the 
corresponding  chlorides,  free  chlorine  will  displace  bromine  from 
bromides.  The  presence  of  free  bromine  in  solution  may  be 
detected  by  the  color  it  imparts  to  carbon  disulphide  or  chloro- 
form. 

Iodine,  atomic  weight,  127,  is  found  as  iodides  in  small  quantities 
in  the  ashes  of  sea  plants,  and  associated  with  sodium  -and  potas- 
sium compounds.  It  is  a  dark  gray  solid  with  the  suggestion  of  a 
metallic  appearance.  In  its  chemical  properties  it  resembles  chlo- 


EXERCISES  285 

rine  and  bromine,  but  it  is  less  active  than  either.  Thus  we  find  that 
with  these  three  elements,  as  the  atomic  weight  increases,  the 
activity  diminishes,  and  the  elements  lose  something  of  their  non- 
metallic  character. 

Iodine  may  be  prepared  by  a  process  analogous  to  that  used  in 
the  preparation  of  chlorine  or  bromine. 

Hydriodic  acid  results  from  the  action  of  moderately  con- 
centrated sulphuric  acid  with  potassium  iodide,  but  only  a  small 
part  of  the  expected  quantity  is  obtained.  The  heat  of  formation 
of  hydriodic  acid  is  so  low  that  it  is  very  readily  oxidized  by  the 
sulphuric  acid.  Sulphur  dioxide,  free  sulphur,  hydrogen  sulphide, 
water,  and  free  iodine  may  all  be  formed  in  this  secondary  action. 

Iodides  have  a  less  heat  of  formation  than  bromides.  Conse- 
quently free  bromine  will  displace  iodine  from  iodides.  Chlorine 
will  do  the  same  thing,  even  more  readily. 

Fluorine,  atomic  weight,  19,  is  the  most  intensely  active  element 
known.  Hydrofluoric  acid  is  a  stable  compound  used  in  etching 
glass. 

The  four  halogens,  considered  as  &  group,  may  be  regarded  as 
the  most  nearly  perfect  example  of  a  chemical  family.  The 
properties  change  in  a  very  definite  and  regular  way  with  the 
change  in  atomic  weight. 

EXERCISES 

1.  How  does  relative  solubility  aid  in  obtaining  bromides 
from  the  brines  of  salt  deposits  ? 

2.  Why  should  bromine  water  be  kept  in  a  dark  place  ? 

3.  Write  the  equations  representing  the  reactions  of  bromine 
with  zinc,  antimony,  and  hydrogen.     Name  the  products  in  each 
case. 

4.  Account  for    the   odor    of    sulphur   dioxide    sometimes 
obtained  when  concentrated  sulphuric  acid  is  added  to  a  bromide. 


286 


THE  HALOGENS 


5.   Prepare  a  table  of  the  halogens  according  to  the  follow- 
ing form : 


a 

b 

c 

d 

e 

Element 

Atomic 

Compounds 

Equations 

Physical 

weight 

found  in 

for  the 

properties 

nature 

preparation 

(Formulas) 

of  element 

/ 

9 

it 

i 

Chemical 

Relative 

Equations 

Stability 

properties 

replacing 

for  the 

of  the 

power  in 

preparation 

hydrogen 

binary 

of  the 

compound 

compounds 

hydrogen 

compound 

6.  A  solution  of  sodium  bromide  is  treated  with  an  excess 
of  silver  nitrate,  and  0.65  gram  of  silver  bromide  is  precipitated. 
What  weight  of  sodium  bromide  was  contained  in  the  original 
solution  ? 

7.  Define  leaching ;  sublimation ;  tincture ;  heat  of  forma- 
tion. 

8.  How  would  you  recover  some  iodine  that  had  become 
mixed  with  sand  ? 

9.  Using  the  formulas  for  potassium  bromide  and  potassium 
iodide,  write  the  three  equations  which  show  the  relative  re- 
placement of  bromine,  chlorine,  and  iodine. 

10.  Why  is  not  sulphuric  acid  used  for  the  preparation  of 
hydriodic  acid  ? 

11.  A  solution  contains  potassium  chloride  and  potassium 
bromide.     How  would  you  show  the  presence  of  the  two  halo- 
gens ? 

12.  What  weight  of  iodine  could  be  obtained  from  150  grams 
of  potassium  iodide?     How  much  sulphuric  acid  would  be 


EXERCISES  287 

needed  for  the  action,  assuming  that  the  acid  "sulphate  of  potas- 
sium is  produced  ? 

13.  Solutions  of  hydriodic   acid   become   dark  colored   on 
standing.     To  what  substance  is  the  dark  color  probably  due  ? 
Explain  the  action  that  produces  it. 

14.  What  laboratory  method  is  equally  good  for  the  prepara- 
tion of  chlorine,  bromine,  and  iodine  ?     Write  the  equations. 

15.  How  would  you  prove  the  presence  of  an  iodide,  employ- 
ing the  starch  test  ? 

16.  State  how  opaque  graduations  could  be  marked  on  a 
blank  gas  measuring  tube. 


CHAPTER   XXV 
CARBON 

306.  Unusual  Character. — Carbon,  though  a  non-metal, 
differs  in  several  important  respects  from  the  other  ele- 
ments of  its  class.     It  forms  almost  numberless  compounds 
with  hydrogen.     These  substances  are  called  hydrocarbons. 
Besides  these,  there  are  many  compounds  that  are  com- 
posed of  carbon,  hydrogen,  and  oxygen  ;  others  are  known 
which  in  addition  contain  chlorine,  bromine,  iodine,  nitro- 
gen, sulphur  or  some  other  element.     There  are  so  many 
of  them  that  the  branch  of  chemistry  which  deals  with  them 
has  a  special  name,  organic  chemistry.     Some  of  the  more 
important   organic   compounds   are    treated  in   Chapters 
XXXVIII  and  XXXIX. 

307.  Importance    of    Carbon    in   Nature.  —  Every    living 
thing,  plant  or  animal,  contains  carbon  in  its  tissues  in  the 
form  of  organic  compounds.     The  higher  plants  always 
contain  a  large  amount  of  cellulose,  which  is  composed  of 
carbon,  hydrogen,  and  oxygen.     Cotton  fiber  in.  the  purest 
form  of  cellulose  known. 

The  muscular  tissue  of  animals  is  composed  of  a  class 
of  bodies  known  as  proteins.  They  contain  carbon,  hydro- 
gen, oxygen,  and  nitrogen,  with  a  very  small  quantity  of 
other  elements.  The  fat  of  animals  is  composed  of  car- 
bon, hydrogen,  and  oxygen. 

308.  Occurrence.  —  In   the  uncombined  *  form    carbon  is 
found  as  coal,  graphite,  and  diamond.     In  addition  to  its 


OCCURRENCE 


289 


a 


FIG.  84.  —  FUELS. 
a,  peat ;  b,  lignite ;  c,  soft  coal ;  d,  anthracite. 

occurrence  in  organic  compounds,  the  element  is  also  found 
in  carbon  dioxide  of  the  atmosphere,  and  very  abundantly 
in  the  carbonates  of  certain  metals,  especially  calcium  and 


290  CARBON 

magnesium.  Marble  and  limestone  are  two  different 
varieties  of  calcium  carbonate.  A  considerable  part  of 
the  earth's  crust  is  made  up  of  these  materials. 

309.  Coal.  —  There  are  two  chief  forms  of  coal  and  sev- 
eral less  important  varieties.  None  of  them  is  pure  car- 
bon. Anthracite  or  hard  coal  (Fig.  84,  d)  contains  over 
80  %  of  uncombined  carbon.  It  usually  contains  a  small 
amount  of  moisture  and  a  variable  quantity  of  incom- 
bustible matter,  the  ash.  Anthracite  coal  is  generally 
graded  in  size  by  screening.  The  smaller  sizes  contain 
more  slaty  impurities  than  large  sizes.  Bituminous  or 
soft  coal  (Fig.  84,  c)  contains  40  <fo  to  60  %  of  uncombined 
carbon.  The  remaining  60  %  to  40  %  is  chiefly  hydrocar- 
bons and  ash.  The  hydrocarbons  can  be  driven  off  as  gases 
by  heating  the  coal  without  access  of  air.  This  operation 
furnishes  a  means  of  making  one  kind  of  illuminating 


Coal  is  fossil  vegetable  matter.  During  a  part  of  the 
earth's  history,  known  in  geology  as  the  carboniferous 
period,  vegetation  flourished  to  a  remarkable  extent. 
Much  of  this  vegetable  matter  was  buried  under  beds  of 
mud  and  sand.  In  this  condition  it  underwent  very  slow 
partial  decomposition.  A  large  part  of  the  hydrogen  and 
oxygen  was  driven  off,  and  the  remainder,  consisting  of 
uncombined  carbon,  was  left  as  coal.  In  anthracite  coal 
the  decomposition  has  proceeded  further  than  in  bitumi- 
nous coal. 

Some  forms  of  coal  contain  even  less  uncombined  carbon 
than  does  the  bituminous  variety.  Cannel  coal  and  lignite 
belong  to  this  class.  Lignite  exhibits  much  of  the  struc- 
ture of  the  wood  from  which  it  was  derived  (Fig.  84,  5). 
Peat  is  moss  or  other  loose  vegetable  matter  that,  to  a 
slight  extent,  has  undergone  a  change  like  that  by  which 


LAMPBLACK 


291 


coal   was   formed    (Fig.   84,  a);     Figure   85   shows   the 
composition  and  heating  value  of  coal,  wood,  and  coke. 


100 


BITUMINOUS 
COAL 


10 


FIG.  85. — COMPOSITION  AND  HEAT  VALUE  OF  COMMON  FUELS. 

OTHER   COMMERCIAL   FORMS   OF   CARBON 

310.  Lampblack.  —  Lampblack,  or  soot,  is  practically 
pure  carbon.  It  is  best  made  by  burning  hydrocarbon 
oils  with  a  limited  supply  of  air.  The  operation  is 
analogous  to  that  which  takes  place  when  a  kerosene  lamp 


292 


CARBON 


smokes.  The  hydrogen  of  the  oil  burns,  but  much  of  the 
carbon  remains  unburned  because  of  the  lack  of  oxygen. 
The  unburned  carbon  is  deposited  as  a  soft,  amorphous, 
slightly  greasy  powder.  Lampblack  is  used  in  making 
paint  and  printers'  ink. 

Large  quantities  of  lampblack  are  made  from  natural 
gas  by  using  machines  of  special  design.     One  of  these 
lampblack  machines  (Salsburgh  patent)  is  shown  in  Fig- 
ure 86.     The  cast- 
iron  disk  (D),  about 
four     feet     in    di- 
ameter, is  mounted 
on  a  hollow  shaft. 
The  burner  (#)  is 
mounted    close    to 
the  disk  in  such  a 
position    that    the 
flames  from  the  tip 
will  be  divided,  half 
of  the  flame  depos- 
iting a  thin  coating 
of   soot,    or    lamp- 
black, on  the  concave  surface,  and  the  other  half  of  the 
flame  depositing  a  thin  coating  on  the  convex  surface  of 
the  disk. 

As  the  disk  revolves  slowly  in  the  direction  of  the 
arrow,  the  scraper  ($)  removes  the  lampblack  from  the 
disk  and  the  black  powder  falls  through  the  hopper  (^T). 
The  lampblack  is  sifted  and  prepared  for  sacking.  The 
top  of  the  disk  is  kept  full  of  running  water,  which  cools 
the  disk  and  then  empties  into  the  hollow  shaft. 


FIG.  86.  —  MANUFACTURE  OF  LAMPBLACK. 


311.  Wood  Charcoal.  —  Wood  charcoal  is  made  by  heat- 
ing wood  without  access  of  air.     To  a  certain  extent  this 


COKE  293 

operation  resembles  the  natural  process  by  which  coal 
was  formed.  The  hydrogen,  oxygen,  nitrogen,  and  some 
of  the  carbon  which  the  wood  contains  pass  off  in  the 
form  of  various  simpler  compounds.  The  operation  is 
known  as  destructive  distillation  (Fig.  145,  §  504).  The 
charcoal  which  remains  is  uncrystallized  in  form,  and 
retains  the  cell  structure  of  the  wood  from  which  it 
was  formed.  Charcoal  is  not  pure  carbon,  as  is  shown  by 
the  fact  that  it  leaves  an  ash  on  burning. 

312.  Boneblack,  or  animal  charcoal,  is  obtained  by  heat- 
ing bones  without   access   of   air.     Bones   contain   both 
mineral  and  animal  matter.     The  animal  matter,  consist- 
ing of  carbon  compounds,  is  converted  into  charcoal  by 
destructive    distillation ;    the    mineral   matter,  which   is 
chiefly  calcium  phosphate,  is  separated  from  the  charcoal 
by  being  dissolved  in  hydrochloric  acid.     Boneblack  is 
extensively  used  for  filtering  purposes.     It  has  the  power 
of  absorbing  both  coloring  matter  and  gases  from  solution. 
This  is  characteristic  of  nearly  all  amorphous  substances. 
Other  forms  of  amorphous  carbon  have  the  same  property 
in  a  less  degree.     The  most  important  use  of  boneblack  is 
in  the  decolorization  of  sugar  and  oils. 

313.  Coke.  —  Coke   is   an   amorphous   form    of   carbon 
obtained   by   the   destructive   distillation    of   bituminous 
coal.     It  is  also  obtained  as  a  by-product  in  the  manu- 
facture of  one  kind  of  illuminating  gas.     In  the  United 
States  nearly  50  million  tons  of  coke  are  produced  yearly 
and  used  in  the  working  of  metals.     The  collection  of 
the  by-products  is  an  important  feature  of  the  operation 
of  the  modern  coke  oven. 

Oil  coke  collects  in  the  retorts  used  in  distilling  petroleum. 
Oil  coke  is  a  good  and  durable  conductor  of  electricity  and 
is  used  for  making  carbon  rods  for  arc  lights. 


294:  CARBON 

'      ALLOTROPIC  FORMS 

314.  —  Among  all  the  varieties  of  carbon  three  distinct 
allotropic  forms  are   recognized.     These  are  amorphous 
carbon  (of  which  lampblack  is  the  purest  form  ordinarily 
obtained),  graphite,  and  diamond.     The  different  varieties 
of  charcoal,  coal,  and  coke  are  impure  forms  of  amorphous 
carbon. 

The  three  allotropic  forms  can  each  be  burned  in  oxygen, 
if  raised  to  a  sufficiently  high  temperature,  with  the  forma- 
tion of  nothing  but  carbon  dioxide.  This  fact  proves  that 
the  three  substances  are  different  forms  of  the  same  ele- 
ment. They  differ  widely  in  physical"  properties  and  in 
the  ease  with  which  they  burn. 

315.  Amorphous  Carbon.  —  As  the  name  implies,  amor- 
phous carbon  is  without  crystalline  structure.     Its  density 
is  low ;  it  is  soft,  and  it  does  not  conduct  an  electric  cur- 
rent very  well.      These   properties   cannot   be   specified 
definitely  because  they  vary  according  to  the  temperature 
to  which  the  element  has  been  subjected.     Amorphous 
carbon  burns  with  comparative  ease. 

316.  Graphite.  —  Graphite  is  a  crystalline  form  of  car- 
bon.    There  are  a  number  of  natural  deposits  of  graphite, 
the  best  coming  from    Ceylon,  Siberia,  and  New  York. 
Graphite  is  now  produced  artificially  by  heating  anthra- 
cite coal  in  an  electric  furnace.     The  crystals  of  graphite 
appear  as  minute  scales  or  plates,  which  present  a  very 
good  sliding  surface.     To  this  property  is  due  the  use 
of  graphite  as  a  lubricant.     Artificial  graphite  may  also 
be  prepared  in  the  form  of  an  extremely  finely 'divided 
powder,  which  will   remain   suspended   in   water   or   oil 
(deflocculated  graphite).     It  differs  from  other  forms  of 


Edward  Goodrich  Acheson  is  the  inventor  of  many  important 
processes  associated  with  the  graphite  and  carbon  compounds. 
He  is  famous  chiefly  as  the  discoverer  of  carborundum,  artificial 
graphite,  and  deflocculated  graphite.  In  connection  with  these 
industries,  he  has  had  a  great  deal  to  do  with  the  development  of 
electric  furnaces.  He  has  invented  graphitized  anodes,  which 
are  much  more  durable  than  carbon  electrodes  in  electrolytic 
furnaces.  To  meet  the  need  for  a  highly  refractory  material  he 
invented  siloxicon,  a  compound  of  carbon,  silicon,  and  oxygen, 
which  resists  fusion  even  at  very  high  temperatures.  .  He  was 
awarded  the  Perkin  Medal  of  the  Society  of  Chemical  Industry  in 
January,  1910. 


CHEMICAL  PROPERTIES  295 

carbon  in  being  very  soft,  in  conducting  the  electric 
current  readily,  and  in  having  a  very  high  kindling 
temperature.  Like  all  forms  of  carbon,  it  has  a  very 
high  melting  point.  This  refractory  nature  of  graphite 
permits  its  use  in  crucibles  for  melting  metals.  Its 
resistance  to  heat  and  its  conducting  power  cause  it 
to  be  extensively  used  for  the  melting  pots  and  electrodes 
of  electric  furnaces.  Graphite  is  also  used  for  making 
lead  pencils.  The  varying  degrees  of  hardness  in  the 
pencil  are  secured  by  mixtures  of  graphite  and  clay. 
Another  use  of  graphite  is  to  prevent  the  formation  of 
scale  in  steam  boilers. 

317.  Diamond.  —  Diamond,  the  third  form,  is  also  a  crys- 
tallized variety  of  carbon.     It  is  found  as  octahedral  crys- 
tals, sometimes  colorless  and  transparent,  sometimes  tinted 
or  even  black.     The  diamond  differs  from  the  other  allo- 
tropic  forms  in  being  extremely  hard.     It  is  the  hardest 
substance  found  in  nature.     Like  graphite,  it  burns  only 
when  heated  to  a  high  temperature.     The  use  of  diamonds 
as  gems  is  due  to  their  great  rarity,  and  to  the  fact  that 
light  in  passing  through  them  is  highly  refracted  so  that 
a  sparkling  play  of  color  results.     This  effect  is  heightened 
by  cutting  the  surface  of  the  stone  into  numerous  facets. 
The  value  of  a*  diamond  depends  largely  on  its  color  and 
its  brilliancy.     Discolored  stones  are  employed  in  cutting 
instruments  for  use  on  hard  materials. 

Microscopic  diamonds  have  been  made  artificially,  but 
such  artificial  diamonds  have  never  been  obtained  clear  or 
of  appreciable  size. 

318.  Chemical  Properties.  —  The  physical  properties   of 
carbon  have  been  described  in  discussing  the  allotropic 
forms  of  the  element. 


296 


CARBON 


a 


None  of  the  forms  of  carbon  reacts  with  either  acids  or 
bases.  They  are  all  insoluble  in  ordinary  solvents.  Melted 
iron  dissolves  carbon  to  a  certain  extent. 

Carbon  has  a  great  tendency  to  unite  with  oxygen  at 
moderately  high  temperatures.  It  not  only  burns  in  oxy- 
gen, but  it  also  unites  with 
the  oxygen  that  is  held  in 
combination  with  other 
elements.  On  this  account, 
carbon  makes  an  excellent 
reducing  agent.  The  reac- 
tion of  carbon  with  copper 
oxide  illustrates  this  prop- 
erty. When  the  mixture  is 
heated  in  a  hard  glass  test 
tube  (Fig.  87,  a)  and  the 
gas  is  led  into  limewater 
(Fig.  87,  5),  a  white  pre- 
cipitate of  calcium  carbon- 
ate indicates  the  presence 
of  carbon  dioxide,  and  me- 
tallic copper  is  produced : 


FIG.  87. 

2CuO  +  C 

Enormous  quantities  of  coke  are  used  in  the  reduction 
of  metals,  particularly  iron,  from  their  ores. 

319.  Reactions  at  High  Temperatures.  —  In  spite  of  the 
fact  that  carbon  forms  so  many  different  compounds  with 
hydrogen,  it  unites  directly  with  this  element  only  at  the 
temperature  of  an  electric  arc,  and  then  very  slowly.  By 
using  the  high  temperature  of  an  electric  furnace,  carbon 
can  be  made  to  unite  with  many  metals  and  some  non- 
metals. 


REACTIONS  AT  HIGH   TEMPERATURES 


297 


The  intense  heat  of  an  electric  furnace  makes  carbon 
react  with  lime  (calcium  oxide),  and  calcium  carbide  is 

formed: 

CaO -H  S  C  — +-  CaC2 .+  CO 

Calcium  carbide  is  used  to  prepare  acetylene,  a  gas  which 
makes  an  excellent  illuminant.  The  gas  is  generated  by 
the  action  of  calcium  carbide  with  water  at  ordinary  tem- 
peratures; 

CaC2  +  2  H2O  — >-  C2H2  +  Ca(OH)2 

Acetylene  is  used  in  bicycle  and  automobile  lamps  and 
in  places  where  the  gas  supply  of  a  city  system  is  not 
available. 

^Asbestos  Board^ 


FIG.  88.  —  LABORATORY  ELECTRIC  FURNACE. 

The  electric  arc  furnace  is  a  device  by  which  a  very 
high  temperature  is  obtained  by  using  a  large  arc  between 
carbon  terminals.  The  arc  consists  of  carbon  vapor, 
which  conducts  the  current  over  the  gap  between  the 
carbons,  and  the  resistance  is  so  great  that  much  heat 
is  developed.  A  temperature  of  about  3000°  C.  is  ob- 
tained. The  reactions  that  occur  in  the  electric  furnace 
are  due  to  the  high  temperature.  The  electric  current 
does  not  directly  play  any  part  in  the  reactions.  A  simple 
laboratory  form  of  furnace  is  shown  in  Figure  88. 

Carborundum  (§  343),  silicon  carbide,  used  as  an  abra- 
sive, is  made  by  heating  sand  (silicon  dioxide)  and  carbon 
in  an  electric  resistance  furnace  (Fig.  104): 

SiO2  +  3  C  — >•  SiC  +  2  CO 


298  CARBON 

When  carbon  is  similarly  heated  in  sulphur  vapor,  the  two 
elements  combine  to  form  carbon  disulphide: 

C     2S  — 


Carbon  disulphide  is  a  heavy,  inflammable  liquid,  with  a 
sweetish  odor,  when  pure,  and  is  valuable  as  a  solvent. 

320.  Uses  of  Carbon.  —  The  uses  of  carbon  have  been 
pointed  out  in  the  discussion  of  the  properties  of  the  various 
forms  of  the  element.  Coal  is  the  principal  source  of  arti- 
ficial heat.  Anthracite  is,  in  general,  the  most  desirable 
kind  of  coal,  because  it  burns  with  practically  no  flame  and 
without  the  formation  of  soot.  It  burns  more  slowly 
and  gives  a  more  uniform  heat  than  does  bituminous  coal. 
The  use  of  anthracite  is  relatively  small;  about  75,000,000 
tons  are  used  annually,  and  its  use  is  confined  to  a  few 
localities. 

There  is  over  seven  times  as  much  bituminous  coal  pro- 
duced as  anthracite;  it  is  much  cheaper,  and,  weight  for 
weight,  produces  more  heat.  Coke  burns  like  anthracite 
coal  and  is  sometimes  used  in  its  place.  In  warm  countries 
charcoal  is  often  the  only  fuel  used.  Many  metals  are  sepa- 
rated from  their  ores  by  the  aid  of  coke  as  the  reducing 
agent.  Iron  is  obtained  in  this  way,  usually  by  the  reduc- 
tion of  hematite,  ferric  oxide.  The  making  of  coke  from 
bituminous  coal  for  this  purpose  is  an  important  industry. 
Charcoal  and  boneblack  are  both  used  to  remove  gases 
and  coloring  matter  from  solutions.  Impure  water  is 
sometimes  passed  through  charcoal  filters  for  purifica- 
tion. This  method,  while  it  may  suffice  for  the  removal 
of  impurities  which  can  be  seen  or  smelled,  is  not  to  be 
relied  upon  for  the  removal  of  disease  germs. 

321.  Flame  of  Candle.  —  We  have  seen  numerous  cases 
of  combustion  or  burning.  When  the  fuel  is  a  solid,  par- 


FLAME   OF  CANDLE 


299 


tides  of  the  fuel  or  of  the  ash  are  often  heated  to  incan- 
descence and  glow.  When  a  stream  of  gas  burns,  a  flame 
is  produced.  This  phenomenon  can  best  be  studied  in  the 
flame  of  a  common  candle. 

When  a  light  is  applied  to  the  tip  of  a  candle  wick,  a  flame 
appears  and  slowly  spreads  down  the  wick  toward  the  candle 
and  upward  about  twice  the  height  of  the  exposed  wick. 
In  a  few  moments  the  flame  becomes 
constant  in  size  and  position  (Fig.  89). 
Starting  about  one  eighth  of  an  inch 
from  the  candle,  the  flame  begins  to  be 
visible,  rounded  at  the  base  and  taper- 
ing to  a  sharp  point  above.  It  entirely 
incloses  the  wick  except  at  the  base 
and  at  the  extreme  tip. 

If  we  examine  the  flame  closely,  we 
see  four  parts.  The  first  is  a  greenish 
blue  portion  of  the  base,  shaped  much 
like  the  cup  of  an  acorn.  This  follows 
the  wick  downward  a  short  distance, 
and  its  upward  extension  is  hidden  by 
the  glare  of  light  within.  Second, 
above  and  within  the  first  green  por- 
tion we  find,  immediately  surrounding 
the  wick,  a  region  dark,  compared  with 
the  more  brilliant  part  above,  but  in  reality  transparent 
and  colorless,  as  is  shown  by  placing  an  object  behind 
it.  This  region  tapers  to  a  point  above  and  is  termed  the 
non-luminous  cone.  Covering  the  cone  just  mentioned  is  a 
bright  cap  known  as  the  luminous  cone.  This  is  the  third 
and  most  conspicuous  region  of  the  flame.  Outside  the 
luminous  cone  we  can  find  the  fourth  region,  which  is 
the  faint  and  scarcely  visible  blue  mantle. 

The  candle  is  composed  of  a  mixture  of  paraffin  and 


FIG.  89. 


300  CARBON 

stearic  acid,  both  of  which  contain  carbon  and  hydrogen. 
The  upper  portion  of  the  candle,  heated  by  the  flame 
above,  melts,  so  that  the  top  becomes  a  cup  holding  a 
small  portion  of  the  melted  fuel.  This  melted  portion  is 
drawn  up  the  wick  by  capillarity,  and  vaporizing,  forms 
the  non-luminous  cone  immediately  surrounding  the  wick. 
If  we  insert  a  tube  into  this  portion  of  the  flame,  we  can 
lead  out  a  quantity  of  vapor  which  condenses  to  a  solid 
similar  to  that  composing  the  candle.  If  we  extend  a 
thin  piece  of  wire  across  the  flame,  we  find  that  it  is  not 
very  warm  near  the  wick ;  in  fact,  the  head  of  a  match 
can  be  placed  there  without  igniting.  There  is  no  com- 
bustion in  this  non-luminous  cone  since  there  is  no  air. 

As  the  vapor  is  carried  upward  by  the  draft  it  becomes 
mixed  with  air  and  combustion  ensues.  This  region  of 
active  burning  is  brilliant  and  hot,  but  not  transparent. 
If  we  place  a  piece  of  cold  porcelain  in  this  portion  of  the 
flame,  or  lead  off  some  of  the  materials  through  a  tube, 
we  find  a  considerable  portion  of  lampblack  (carbon)  and 
moisture.  The  carbon  while  in  the  luminous  cone  is 
heated  to  incandescence. 

Since  the  combustible  vapors  are  slowly  mixed  with  air, 
the  materials  may  move  considerable  distances  from  the 
wick  before  they  meet  sufficient  oxygen  to  burn ;  hence 
when  a  large  wick  is  used,  the  bulk  of  vapor  makes  an  ex- 
tensive region  of  flame.  Indeed,  the  upper  extremity  is 
often  so  far  removed  that  its  temperature  falls  below  the 
kindling  temperature  of  the  combustible  materials. 
These  escape  unburned  and  the  flarrfe  smokes. 

In  the  outer  portion  of  the  flame  the  conditions  are  re- 
versed, in  that  the  air  is  in  excess.  Here  the  combustion 
is  complete,  but  usually  only  a  small  amount  of  combusti^ 
ble  material  reaches  this  pale  outer  portion.  This  mate- 
rial, if  drawn  out  by  a  tube,  is  found  to  be  principally  air 


GAS  FLAMES  301 

mixed  with  products  of  combustion.  The  pale  green  cup 
below  is  similarly  constituted ;  but  because  of  its  position 
below  the  principal  region  of  combustion  and  its  nearness 
to  the  cool  wick  and  candle,  it  is  not  so  warm  as  the  blue 
mantle  above. 

The  wick  is  made  of  cotton  and  is  proportioned  to  the 
quantity  of  material  to  be  burned.  The  cool  stream  of 
liquid  drawn  up  the  wick  protects  it  from  burning,  and, 
at  the  same  time,  prevents  the  flame  extending  down  to 
the  candle.  As  the  candle  material  is  vaporized,  the  wick 
chars  somewhat  but  does  not  burn,  since  there  is  no  oxy- 
gen in  its  immediate  vicinity.  In  braiding  the  wick,  one 
of  the  threads  is  drawn  tighter  than  the  others,  so  that 
the  wick,  when  free  from  the  candle-stuff,  is  drawn  over 
to  one  side  of  the  flame.  This  braiding  of  the  wick 
brings  the  tip  into  the  outer  zone  of  combustion,  where  it 
burns  so  far  as  air  is  available, 
rotating  as  the  candle  shortens 
and  practically  maintaining  a  uni- 
form  length.  This  is  why  mod- 
ern candles  do  not  need  to  be 
trimmed. 


INCOMPLETE  COMBUSTION 
SOLID  CARBON  PRESENT 
LUMINOUS 


Gas  Flames. — In  the  ordi- 
nary gas  flame  (Fig.  90),  as  well 

as  in  the  candle  flame,  the  four 

T        -,  11.1          FIG.  90.  —  FISHTAIL  FLAME. 

regions  are  clearly  marked:    the 

region  of  fuel,  or  non-luminous  cone;  the  luminous 
cone,  or  region  of  luminosity ;  outside  and  lower  regions 
of  combustion  with  an  excess  of  air.  The  size  and 
shape  of  gas  flames  depend  largely  on  the  tip  of  the  burner. 
In  a  Bunsen  burner  (§  29)  we  can  adjust  the  proportions 
of  gas  and  air  so  that  there  shall  be  no  excess  of  either. 
Then  the  flame  will  appear  to  have  two  regions,  a  lower 


302  CARBON 

cone    where   no    combustion    is    apparent   and    the    cap 
above. 

In  the  ordinary  flame,  we  find  the  position  of  maximum 
temperature  somewhat  above  and  outside  the  light-giving 
materials.  A  very  large  part  of  the  energy  passes  off  as 
heat  and  only  a  very  small  per  cent  is  converted  into 
light.  If  the  solids  giving  light  could  be  placed  above  or 
in  the  region  of  maximum  temperature,  they  would  evi- 
dently be  hotter  and  give  more  light.  Auer  von  Welsbach 
accomplished  this  by  placing  a  mantle  composed  of  a  net 
of  infusible  and  incombustible  materials  in  the  outer  por- 
tion of  the  flame  of  a  Bunsen  burner.  The  materials  are 
heated  to  incandescence  and  produce  the  brilliant  light 
given  by  the  Welsbach  burner. 

SUMMARY 

Carbon  is  a  non-metallic  element,  characterized  by  the  enormous 
number  of  compounds  it  forms  with  the  non-metallic  elements, 
especially  hydrogen,  oxygen,  and  nitrogen. 

Carbon  is  an  inert  element  at  ordinary  temperatures  ;  at  higher 
temperatures  it  combines  readily  with  oxygen  and  with  a  few  other 
elements ;  at  the  temperature  of  the  electric  furnace  it  reacts 
with  lime,  forming  calcium  carbide. 

Amorphous  carbon,  graphite,  and  diamond  are  the  three  allo- 
tropic  forms  of  carbon.  These  allotropic  forms  differ  widely  in 
physical  properties,  but  all  yield  the  same  product  when  burned  in 
sufficient  oxygen. 

Carbon  is  found  combined  in  the  tissues  of  every  living  thing, 
in  the  carbon  dioxide  of  the  atmosphere,  and  in  metallic  carbon- 
ates. Uncombined,  it  occurs  as  coal,  graphite,  and  diamond. 

Anthracite  coal  is  nearly  all  carbon ;  bituminous  coal  is  about 
two  thirds  carbon  and  one  third  hydrocarbons ;  cannel  coal  and 
lignite  are  poor  in  uncombined  carbon. 


EXERCISES  303 

The  uses  of  the  forms  of  carbon  are : 
Coal :  fuel  and  manufacture  of  illuminating  gas  ; 
Lampblack  :  paint  and  printers'  ink  ; 
Wood  charcoal :  fuel  and  filtering  ; 
Boneblack  :  filtering  and  decolorizing  sugar  and  oils ; 
Coke :  fuel,  ore  reducer,  and  manufacture  of  water  gas ; 

Graphite  :  lead  pencils,  lubricant,  crucibles,  and  electrodes  for  high 

temperatures ; 
Diamond  :  gem  and  abrasive. 

The  four  portions  of  a  candle  flame  are  the  greenish  blue  region 
at  the  base,  the  non-luminous  cone,  the  luminous  cone,  and  the  blue 
mantle.  The  ordinary  gas  flame  has  four  similar  portions,  while 
that  of  the  Bunsen  burner  appears  to  have  but  two  —  the  lower 
cone  and  the  surrounding  conical  cap  above. 

EXERCISES 

1.  Tell  how  the  carbon  in  your  muscular  tissue  is  indirectly 
derived  from  the  air. 

2.  How  does  anthracite  coal  differ  from  bituminous  coal  in 
appearance  and  in  chemical  composition  ? 

3.  Why  does  soft  coal  make  such  a  smoky  fire  ? 

4.  Why  is  anthracite  coal  preferred  for  household  use  ? 

5.  Explain  why  fence  posts  are  sometimes  charred  at  the 
end  before  being  placed  in  the  ground. 

6.  What    properties    of    lampblack    make   it    suitable    for 
printers'  ink  and  for  paint  ? 

7.  What  kind  of  carbon  is  used  in  batteries  ? 

8.  State  briefly  how  you  could  distinguish  between  pulver- 
ized charcoal  and  manganese  dioxide. 

9.  What  three  conditions  are  necessary  for  ordinary  burn- 
ing? 


304  CARBON 

10.  Why  does  water  put  out  a  fire  ? 

11.  Why  is  a  candle  extinguished  by  blowing  ? 

12.  In  working  with  compressed  air  it  is  found  that  com- 
bustible materials  burn  more  readily  than  usual.     Explain. 

•'/MS.  How 'many  liters  of  oxygen  are  required  for  the  complete 
combustion  of  10  liters  of  acetylene  gas  ?  How  many  liters  of 
air  are  required  ? 

14.  Indicate  by  a  diagram  the  principal  parts  of  a  candle 
flame.  Compare  these  parts  with  respect  to  temperature  and 
light-producing  properties.  Why  is  a  flame  extinguished  by 
surrounding  it  with  carbon  dioxide  ? 

15.  Why  is  the  flame  of  a  Bunsen  burner  hotter  with  the 
holes  open  than  when  they  are  closed  ?  Is  the  total  heat  in- 
creased ? 

16.  Why  does  not  the  flame  of  a  Bunsen  burner  extend  down 
the  tube  to  the  base  ? 

17.  If  a  taper  is  held  over  a  gas  burner,  a  flame  may  be 
maintained  several  inches  above  the  burner  without  "  striking 
back  "  to  the  burner.     Explain. 

18.  Describe  the  structure  and  the  operation  of  a  Welsbach 
light. 


CHAPTER  XXVI 
OXIDES  OF  CARBON 

CARBON   DIOXIDE 

323.  Occurrence.  —  There     are    three    very    important 
sources  of  carbon  dioxide:  the  decay  of  vegetable  and 
animal  matter;  the  oxidation  constantly  going  on  in  ani- 
mals, and  to  a  much  smaller  extent  in  plants;  the  com- 
bustion of  all  ordinary  fuels,  such  as  wood,  coal,  and  gas. 
These  fuels  consist  largely  of  carbon;  this,  on  burning, 
combines  with  oxygen,  forming  carbon  dioxide: 

C  +  O2  — >-  CO2 

Hence  the  gas  is  always  present  in  the  air,  usually  to  the 
amount  of  four  parts  in  ten  thousand  (§  231).  This  per- 
centage would  be  much  higher  were  it  not  for  the  fact 
that  plants  are  constantly  taking  in  carbon  dioxide,  build- 
ing the  carbon  into  their  tissues,  and  returning  the  oxygen 
to  the  air. 

Natural  waters  also  very  commonly  contain  carbon 
dioxide;  in  some  spring  waters  the  gas  is  dissolved  in  such 
quantities  that  they  are  effervescent,  that  is,  they  give  off 
gas  in  bubbles  unless  kept  in  tightly  closed  vessels.  Car- 
bon dioxide  is  also  given  off  by  volcanoes  and  from  other 
subterranean  sources,  and  from  fermenting  liquids.  It  is 
sometimes  found  in  coal  mines,  where  it  is  known  as  choke 
damp. 

324.  Preparation.  —  Carbon  dioxide  is  most  conveniently 
prepared   in  a  pure  state  by   the  action  of  a  carbonate 

305 


306 


OXIDES  OF  CARBON 


with  an  acid  (Fig.  91).     Calcium  carbonate,  which  occurs 
abundantly  in  the  forms  of  limestone,  marble,  and  chalk,  is 

used  on  account  of  its  cheap- 
ness; and,  on  a  manufactur- 
ing scale,  sulphuric  is  the 
acid  selected.  But  this  is 
not  convenient  when  the 
carbon  dioxide  is  needed  in 
small  quantities,  as  in  the 
laboratory,  because  the  cal- 
cium sulphate  which  is 
formed  in  the  action  io  in- 


FIG.  91.  —  PREPARATION  OF  CARBON 

DIOXIDE. 
a,  generator ;  b,  collecting  bottle. 


soluble  and  remains  as  a 
coating  on  the  pieces  of  car- 
bonate, thus  hindering  the 
action.  Hydrochloric  acid  gives  good  results  because 
calcium  chloride  is  quickly  soluble  in  water.  The  equa- 
tion representing  the_  action  is  : 


CaCCL  +  2  HC1 


CaCL  +  H«O  +  CO. 


To  remove  any  hydrochloric  acid  that  may  be  carried  over 
the  gas  is  allowed  to  bubble  through  water.  The  gas  is 
collected  by  downward  displacement  of  air  or  over  water. 

325.  Physical  Properties. — Carbon  dioxide  is  a  colorless 
gas  with  little  taste  or  odor.  It  is  about  one  and  one  half 
times  as  dense  as  air,  so  that  it  can  be  poured  from  one 
vessel  to  another  like  water.  Carbon  dioxide  is  some- 
times given  off  from  soil  and  water;  and  in  wells,  caves, 
and  mines  it  frequently  collects,  because  the  lack  of  air 
movement  permits  the  relatively  heavy  gas  to  settle  and 
accumulate. 

The  gas  is  soluble  in  water,  which  dissolves  its  own 
volume  at  ordinary  temperatures.  Under  increased  pres- 


PROPERTIES  OF  CARBON  DIOXIDE 


307 


sure,  water  dissolves  a  greater  weight  of  the  gas;  if  the 
pressure  is  removed,  the  gas  is  slowly  given  off,  since 
the  weight  of  a  gas  which  a  given  volume  of  a  liquid  will 
dissolve  is  directly  proportional  to  the  pressure.  An 
illustration  of  this  property  is  found  in  effervescent 
beverages,  which  always  contain  dissolved  carbon  dioxide. 
Carbon  dioxide  can  be  liquefied  by  pressure  at  ordinary 
temperatures  and  the  liquid  is  sold  in  steel  cylinders. 


FIG.    92.  —  CANDLES    SUCCESSIVELY    EXTINGUISHED    BY    POURING    CARBON 
DIOXIDE  INTO  V-SHAPED  TROUGH. 

326.  Chemical  Properties.  —  Carbon  dioxide  is  chemically 
inactive  toward  most  substances.  It  is  the  product  of  the 
complete  oxidation  of  carbon,  an  action  which  occurs  with 
the  liberation  of  a  great  amount  of  energy.  Carbon 
dioxide  can,  however,  be  reduced  by  very  active  reducing 
agents,  such  as  burning  potassium,  sodium,  or  magnesium. 
These  elements  unite  with  oxygen  and  set  carbon  free. 


308  OXIDES   OF  CARBON 

Carbon  dioxide  does  not  support  combustion  (Fig. 
92).  This  property  makes  it  very  valuable  for  use  in  ex- 
tinguishing fires. 

327.  Carbon  Dioxide  in  Air.  —  Under  certain  conditions 
the  amount  of  carbon  dioxide  in  the  air  may  go  much 
above  the  normal.     This  does  not  interfere  with  either 
combustion  or  the  process  of  breathing,  unless  the  increase 
in  carbon  dioxide  in  the  air  is  accompanied  by  a  corre- 
sponding decrease  in  oxygen,  which  may  or  may  not  be  the 
case.     The  per  cent  of  carbon  dioxide  in  the  air  is,  there- 
fore, not  a  measure  of  its  fitness  for  breathing,  except  as 
an  index  to  ventilation. 

From  the  standpoint  of  its  relation  to  life,  the  most  im- 
portant reaction  of  carbon  dioxide  is  one  that  occurs  in 
the  leaves  of  plants,  whereby  it  acts  with  water  under  the 
influence  of  light  and  chlorophyl,  forming  starch  and  set- 
ting free  oxygen : 

6  C02  +  5  H20  -+  6  02  +  C6H1005 

The  water  in  this  reaction  comes  from  the  roots  of  the 
plant,  and  the  carbon  dioxide  is  taken  from  the  air. 

328.  Carbonic  Acid.  —  The  solution  of  carbon  dioxide  has 
a  slightly  acid  reaction  and  forms  carbonates  with  bases. 
Carbonic  acid  is  extremely  unstable,  and,  like  ammonium 
hydroxide,  has  never  been  isolated,  but  the  formation  of 
carbonates  indicates  the  presence  of  hydrogen  ions   and 

ions.     We  may  write  the  equation : 

+  +  C03- 

Carbon  dioxide  passed  into  a  solution  of  a  base 
produces  the  corresponding  carbonate.  As  calcium  car- 


HARD    WATERS  309 

bonate  is  insoluble,  calcium  hydroxide  (limewater)  is  used 
as  a  test  for  the  presence  of  carbon  dioxide.  When  carbon 
dioxide  is  first  passed  into  limewater,  it  becomes  milky,  and 
on  standing  the  precipitate  of  calcium  carbonate  settles : 

H2C03  +  Ca(OH)2  — >-  CaCOg  +  2  H2O 

If  the  passage  of  carbon  dioxide  is  continued,  the  precipi- 
tate dissolves.  This  is  because  it  has  been  converted  into 
calcium  bicarbonate,  which  is  soluble  in  water : 

H2CO3  +  CaCO3 — >-  CaH2(CO3)2 

329.  Hard  Waters.  —  The  solubility  of  calcium  carbonate 
in  water  containing  an  excess  of  carbon  dioxide  explains 
the  formation  of  the  kind  of  hard  water  that  is  found  in 
regions  where  limestone  is  abundant.  The  surface  water, 
becoming  charged  with  carbon  dioxide  from  decay  going 
on  in  the  soil,  dissolves  some  of  the  limestone,  convert- 
ing it  into  calcium  bicarbonate.  If  an  attempt  is  made 
to  use  soap  with  such  water,  it  is  found  difficult  to  ob- 
tain a  lather,  as  the  calcium  ions  react  with  the  soap  to 
form  an  insoluble  soap.  By  boiling  hard  water  of 
this  kind,  part  of  the  carbon  dioxide  is  driven  off  and  the 
calcium  bicarbonate  is  converted  into  calcium  carbonate : 

CaH2(CO3)2— -^CaCOg  +  CO2  +  H2O 

The  carbon  dioxide  escapes  and  the  calcium  carbonate  is 
precipitated.  If  the  rocks  contain  magnesium  carbonate, 
this  may  be  converted  into  the  bicarbonate  and  dissolved 
in  the  same  way  as  with  the  calcium  compound,  and  the 
water  may  be  softened  by  the  same  means.  Water  con- 
taining such  dissolved  bicarbonates  is  called  water  of  tem- 
porary hardness.  Water  of  permanent  hardness  generally 
contains  sulphates  of  calcium  and  magnesium  and  cannot  be 
softened  by  boiling. 


310 


OXIDES   OF  CARBON 


330.  Uses  of  Carbon  Dioxide.  —  As  an  easily  soluble,  non- 
poisonous  gas,  carbon  dioxide  is  extensively  employed  in 
the  manufacture  of  effervescent  beverages.  Soda  water 
is  water  into  which  carbon  dioxide  has  been  forced  under 
pressure  (60  to  150  Ibs.),  and  effervesces  when  drawn. 
Liquids  bottled  during  fermentation,  as  champagne  and 
kumiss,  effervesce  for  a  similar  reason.  Seltzer,  vichy, 
and  other  mineral  waters  are  produced  artificially  by 

charging  solutions  whose 
composition  is  similar 
to  that  of  the  original 
spring. 

One  type  of  fire  ex- 
tinguishers(}?ig.  93)  con- 
tains a  device  for  gen- 
erating carbon  dioxide 


FIG.  93.  —  FIRE  EXTINGUISHER. 


;§3E3==  .,,  , 

rapidly,    as    by   mixing 

sulphuric  acid  with  a 
solution  of  sodium  car- 
bonate when  the  appa- 
ratus is  inverted.  The 
pressure  of  the  gas 
forces  a  stream  of  water 
that  contains  bubbles  of  carbon  dioxide  on  the  fire.  In 
some  chemical  engines  the  pressure  of  carbon  dioxide  is 
sometimes  used  to  throw  a  stream  of  water. 

The  raising  of  bread  and  most  other  forms  of  leavening 
generally  depend  on  the  expansion  of  bubbles  of  carbon 
dioxide  by  heat.  The  carbon  dioxide  is  generated  by 
yeast  or  by  the  reaction  of  sodium  bicarbonate  (baking 
soda)  and  a  material  of  acid  reaction ;  for  example,  acid 
potassium  tartrate,  HKC4H4O6  (cream  of  tartar): 


NaHC03  +  HKC4H406 


+HO  +  CO, 


PREPARATION  OF  CARBON  MONOXIDE 


311 


The  compound,  sodium  potassium  tartrate,  NaKC4H4O6, 
is  known  as  Rochelle  salts. 

Liquefied  carbon  dioxide  is  used  at  soda  fountains  to 
make  soda  water.  It  is  also  used  like  ammonia  in  re- 
frigerating processes,  particularly  on  ocean  vessels  where 
the  escape  of  ammonia  would  be  dangerous. 


CARBON   MONOXIDE 

331.  Preparation.  —  Carbon  monoxide  differs 
bon  dioxide  in  containing  one  atom  of  oxygen 
two.  It  can  be  prepared  by 
the  reduction  of  carbon  di- 
oxide. This  can  be  accom- 
plished by  passing  a  current 
of  carbon  dioxide  over  carbon 
heated  to  redness  in  an  iron 
tube.  The  carbon  acts  as  a 
reducing  agent: 


from  car- 
instead of 


To  Chimney 


CO 


2  CO 


This  action  takes  place  in  a 
coal  fire.  The  carbon  dioxide, 
formed  near  the  bottom,  is 
reduced  by  the  hot  coal  above 
to  carbon  monoxide,  which  is 
often  seen  burning  at  the  top 
of  the  fire  (Fig.  94). 

In  the  laboratory,  carbon 
monoxide  is  best  made  by  the 
decomposition  of  formic  acid  (Fig.  95).  Warm  sul- 
phuric acid  is  slowly  dropped  into  formic  acid.  The  sul- 
phuric acid,  by  its  dehydrating  power,  induces  an  action  as 
follows : 

HCH02— 


FIG.    94.  —  CHEMICAL   ACTION    IN 
A  COAL  STOVE. 


312 


OXIDES   OF  CARBON 


The  water  is  absorbed  by  the  sulphuric  acid.  Oxalic  acid 
gives  carbon  dioxide  by  a  similar  decomposition  when 
treated  with  sulphuric  acid: 


CO  +  C0 


H20 


H2C204 

In  this  case  it  is  necessary  to  remove  the  carbon  dioxide 
from  the  mixed  gases  by  passing  them  through  a  concen- 
trated solution  of  potassium  hydroxide. 


FIG.  95.  —  PREPARATION  OF  CARBON  MONOXIDE. 

a,  beaker  for  warming  sulphuric  acid  ;  b,  dropping  funnel ;  c,  flask  contain- 
ing formic  acid  ;  d,  collecting  bottle. 

332.  Physical  Properties.  —  Carbon  monoxide  is  a  color- 
less, odorless  gas.  It  is  slightly  lighter  than  air  and  is 
nearly  insoluble  in  water.  It  is  extremely  poisonous  ; 
a  very  small  percentage  in  the  air  causes  headache,  and  a 
larger  amount  may  cause  death. 


333.   Chemical  Properties.  —  Under  ordinary   conditions 
the  monoxide  burns  in  air  with  a  blue  flame.     If  both  the 


WATER   GAS  313 

carbon  monoxide  and  the  air  are  absolutely  dry,  however, 
combustion  does  not  take  place.  Carbon  monoxide  acts 
as  a  powerful  reducing  agent.  The  reduction  of  iron 
oxide  in  a  blast  furnace  is  largely  due  to  it. 

334.  Physiological  Properties.  —  Carbon    monoxide    pre- 
vents the  oxygen  of  the  air  from  uniting  with  the  haemo- 
globin of  the  red  blood  corpuscles,  by  entering  itself  into 
combination  with  the  haemoglobin  to  form  a  stable  com- 
pound.    It  is  because  of  this  action  that  a  comparatively 
small  amount  of  the  gas  will  cause  death.     The  compound 
formed  in  the  corpuscles  has  a  brilliant  red  color,  and  is  so 
stable  that  it  can  be  detected  in  a  body  years  after  death. 
Carbon  monoxide  is  an  important  poison  in  illuminating 
gas  and  the  gas  escaping  from  stoves.     Fortunately  in 
these  cases  it  is  associated  with  compounds  having  pro- 
nounced odors.     In  spite  of  this  fact,  sickness  and  death 
are  frequently  caused  by  carbon  monoxide  poisoning. 

335.  Water  Gas.  —  In  addition  to  its  use  as  a  means 
of  reducing    metallic  oxides,    carbon   monoxide  is  com- 
mercially important  as   a  constituent  of  the    variety    of 
illuminating  gas  known  as  water  gas.     This  is  produced 
by  the  reduction  of  steam  by  heated  carbon  : 

C  +  H0—  ^H 


As  this  mixture  of  carbon  monoxide  and  hydrogen  burns 
with  a  non-luminous  flame,  the  gas  must  be  enriched  by 
an  addition  of  gaseous  hydrocarbons  obtained  from  pe- 
troleum if  the  gas  is  to  be  used  for  lighting. 

Figure  96  shows  a  generator  in  which  the  two  opera- 
tions are  combined.  Coal  in  the  lower  chamber  is  burned 
to  incandescence  by  a  blast  of  air.  At  first,  the  hot  gases 
pass  up  through  the  side  pipe  and  out  at  C.  But  after 


314 


OXIDES   OF  CARBON 


combustion  is  well  under  way  they  are  led  down  through 
the  carburetor,  and  up  through  the  superheater  and  out  at 
O1 '.  The  brick  checker  work  which  these  two  chambers  con- 
tain is  thus  heated  to  the  desired  temperature.  When  this 

is  reached,  the  first  part 
of  the  operation,  called  the 
blow,  is  terminated.  It 
lasts  about  5  minutes. 

Then  steam  instead  of 
air  is  blown  through  the 
incandescent  coal,  and 
carbon  monoxide  and  hy- 
drogen are  formed.  Oil 
is  sprayed  into  the  car- 
buretor, and  is  decomposed 
by  the  heat  into  gases  of 
high  illuminating  power 
that  mix  with  the  unen- 
riched  gas0  The  decom- 
position ot  the  oil  vapor 
is  continued  and  the  mix- 
ture made  uniform  in  the 
superheater.  The  en- 
riched gas  passes  out  the 
side  pipe  at  the  top  of 
the  superheater.  This 
second  operation,  known  as  the  run,  also  lasts  about 
5  minutes  and  alternates  with  the  blast. 

The  various  valves  (V)  shown  in  the  diagram  control 
the  passage  of  the  gases  so  that  the  temperature  in  any 
part  of  the  generator  can  be  perfectly  regulated. 

336.  Producer  gas,  containing  carbon  monoxide  as  its  es- 
sential constituent,  is  an  important  cheap  industrial  fuel. 


FIG.  96.  —  WATER  GAS  GENERATOR. 


PRODUCER   GAS 


315 


It  is  made  by  forcing  a  carefully  regulated  supply  of  air 
through  incandescent  coal : 


2C  +  0, 


2  CO 


The  gas  contains,  in  addition  to  carbon  monoxide,  a  large 
amount  (63%)  of  nitrogen  and  a  small  amount  of  hydro- 
carbons obtained  from  the 
coal. 

The  generator,  shown  in 
Figure  97,  resembles  an 
ordinary  stove  in  con- 
struction and  operation. 
Carbon  dioxide,  formed 
at  the  bottom,  is  reduced 
to  the  monoxide  while 
passing  through  the  hot 
upper  layers  of  coal.  In 


some  cases,  about  6%  of 
steam  is  blown  in  with  the 
air,  and  a  product  is  ob- 
tained which  contains  a  small  amount  of  hydrogen. 

Producer  gas  is  often  obtained  as  a  by-product  from 
blast  and  other  furnaces,  and  its  use  is  a  considerable 
factor  in  the  economy  of  the  plant. 


FIG.  97.  —  GAS  PRODUCER. 


SUMMARY 

Carbon  dioxide  is  formed  in  -the  vital  processes  of  plants  and 
animals,  and  in  ordinary  combustion. 

It  is  prepared  commercially  by  the  reaction  of  acids  with  car- 
bonates. 

Carbon  dioxide  is  colorless,  slightly  soluble  in  water,  and  suffo- 
cating, but  not  poisonous. 


316  OXIDES  OF  CARBON 

One  liter  (standard  conditions)  weighs  1.98  grams. 

It  reacts  with  soluble  bases,  forming  carbonates.  Small  quanti- 
ties render  limewater  turbid  ;  excess  of  the  dioxide  causes  the  pre- 
cipitate to  dissolve.  Such  a  solution  is  temporary  hard  water ; 
boiling  expels  the  excess  of  carbon  dioxide,  and  the  calcium  car- 
bonate again  separates. 

Carbon  dioxide  is  used  in  charging  beverages,  in  fire  extinguish- 
ers, and  in  ice  machines. 

Carbon  monoxide  is  formed  by  : 

(1)  the  incomplete  combustion  of  carbon; 

(2)  the  reduction  of  the  dioxide  ; 

(3)  the  reaction  of  steam  and  red-hot  coal. 

Carbon  monoxide  is  lighter  than  air,  and  is  very  poisonous. 
One  liter  (standard  conditions)  weighs  1.26  grams. 

It  burns  with  a  pale  blue  flame,  forming  the  dioxide. 

Water  gas,  used  as  an  illuminant,  is  obtained  by  (1)  the  action 
of  steam  on  incandescent  coal,  and  (2)  enriched  by  the  addition 
of  gases  derived  from  petroleum.  Action  (1)  gives  carbon  mon- 
oxide and  hydrogen ;  action  (2)  hydrocarbons  of  high  illuminating 
power. 

Producer  gas,  used  only  as  a  fuel,  is  made  by  the  action  of  air, 
sometimes  mixed  with  a  small  amount  of  steam,  on  incandescent 
coal.  Its  active  constituents  are  carbon  monoxide  and  small 
amounts  of  hydrogen  and  hydrocarbons.  A  large  amount  of  inert 
nitrogen  remains  in  the  gas. 

EXERCISES 

1.  How  can  it  be  shown  that  there  is  carbon  dioxide  in  the 
air? 

2.  Give  three  ways  in  which  carbon  dioxide  is  produced  in 
nature.     How  is  it  commonly  made  in  the  laboratory  ?     Write 


EXERCISES  317 

the  equation.     Write  an  equation  illustrating  the  use  of  the 
same  process  but  with  different  materials. 

3.  Why  is  hydrochloric  acid  preferred  to  sulphuric  acid  in 
preparing  carbon  dioxide  from  calcium  carbonate  ? 

4.  Why  does  soda  water  effervesce  when  taken  from  the 
tank? 

5.  Describe  three  important  uses  of  carbon  dioxide,   and 
state  the  properties  on  which  each  use  depends. 

6.  Explain  how  a  fire  extinguisher  puts  out  a  fire. 

7.  Describe  the  natural  formation  of  hard  water.     State 
how  it  may  be  softened.     How  does  hard  water  differ  from 
distilled  water  in  its  action  on  a  soap  solution  ? 

8.  Why  is   rainwater   preferred  for  washing  purposes  in 
limestone  regions  ? 

9.  How  could  you  prove  that  there  is  carbon  in  alcohol  ? 

10.  By  what  process  may  carbon  monoxide  be  obtained  from 
carbon  dioxide  ?     Account  for  the  explosions  that  frequently 
occur  in  coal  stoves  shortly  after  coal  is  added.     State  how 
these  explosions  may  be  avoided. 

11.  How  could  you   distinguish  carbon   dioxide  from   the 
monoxide  ? 

12.  Write  the  equation  for  the  reaction  you  would  expect  if 
carbon  monoxide  were  passed  over  hot  copper  oxide. 

13.  How  would  you  determine  whether  a  gas  was  hydrogen 
or  carbon  monoxide  ? 

14.  Why  is  it  that  such  a  large  percentage  of  the  cases  of 
asphyxiation  from  water  gas  result  fatally  ? 

15.  Explain  why  cases  of  asphyxiation  occur  after  coal  stoves 
have  been  filled  and  left  for  the  night. 

16.  Calculate  the  weight  of  steam  that  could  be  decomposed 
by  a  ton  of  incandescent  coke  containing  90  %  carbon. 


318  OXIDES   OF  CARBON 

17.  How  many  grams  of  calcium  nitrate  can  be  obtained  by 
adding  sufficient  nitric  acid  to  15  grams  of  pure  calcium  car- 
bonate ? 

18.  (a)  What  weight  of  carbon  dioxide  is  required  to  pre- 
cipitate completely  as  calcium  carbonate  the  calcium  in  1  gram 
of  calcium  hydroxide  ? 

(6)  What  volume  will  this  weight  of  carbon  dioxide  occupy 
at  room  temperature  and  760  mm.?  (One  liter  of  C02  at 
room  temperature  and  760  mm.  weighs  1.90  grams.) 

(c)  Assuming  that  each  bubble  of  carbon  dioxide  contains  0.3 
c.c.,  how  many  bubbles  will  be  required ;  and  assuming  that 
they  pass  at  the  rate  of  5  per  second,  how  long  will  the  op- 
eration take  ? 

19.  How  many  grams  of   sulphuric  acid  (H2SO4)  reacting 
with  an  excess  of  sodium  carbonate  (Na^CC^)  are  required  to 
produce  200  grams  of  carbon  dioxide  (C02)  ? 

20.  Calculate  how  many  liters  of  carbon  dioxide,  at  standard 
conditions,  can  be  obtained  by  treating  45  grams  of  pure  marble 
with  acid. 

21.  It  has  been  calculated  that  an  average  man  exhales  464.5 
liters  (standard  conditions)  of  carbon  dioxide  in  a  day.     Cal- 
culate how  many  grains  of  starch  a  plant  could  make  from  this. 

22.  Carbon  monoxide  passed  over  warm  calcium  hydroxide 
reacts  : 

CO  +  Ca(OH)2  — *-  H2  +  CaC03 

How  does  the  volume  of  carbon  monoxide  compare  with  that 
of  the  hydrogen? 


CHAPTER  XXVII 
SILICON  AND  BORON 

337.  Silicon.  —  Silicon,  next  to  oxygen,  is  the  most 
abundant  element  in  the  earth's  crust.  Nearly  all  the 
common  rocks  are  silicon  compounds.  Silicon,  as  an 
element,  is  of  little  practical  importance.  Like  carbon,  it 
exists  in  allotropic  forms.  It  is  prepared  by  reducing 
silica  with  aluminum.  A  small  percentage  of  silicon  is 
found  in  cast  iron  and  traces  of  it  in  steel.  It  is  used  as 
a  detector  in  wireless  telegraphy. 


Courtesy  of  the  Brooklyn  Museum. 

FIG.  98.  —  MASS  OF  QUARTZ  CRYSTALS. 

338.  Varieties  of  Silicon  Dioxide.  —  Silicon  dioxide,  or 
silica,  SiO2,  is  the  most  common  compound  of  silicon.  It 
is  found  in  many  varieties,  which  differ  in  color  and  struc- 
ture owing  to  minute  quantities  of  impurities,  and  to  con- 
ditions under  which  they  are  formed.  Quartz,  the  most 
common  form,  crystallizes  in  hexagonal  prisms,  sur- 
mounted by  a  pyramid  (Figs.  27  and  98).  Clear  crystal- 
line varieties  are  known  as  rock  crystal;  purple  varieties 
as  amethyst.  Rose  quartz,  milky  quartz,  and  smoky 

319 


320 


SILICON  AND  BORON 


quartz,  or  cairngorm  stone,  are  other  colored  varieties  of 
silicon  dioxide,  which,  indeed,  is  found  in  all  shades  and 
tints,  on  account  of  the  presence  of  minute  quantities  of 
impurities.  Chalcedony  is  cryptocrystalline  and  waxlike. 
Onyx  and  agate  are  varieties  of  chalcedony.  Jasper  and 
flint  are  other  forms  of  silica.  Opal  is  a  hydrated  form. 

The  shells  of  diatoms  and  many  other  microscopic  or- 
ganisms are  siliceous,  and  deposits  of  these  comprise  the 

infusorial  or  diatoma- 
ceous  earth  (Fig.  99). 
Sand  is  water- worn  sili- 
con dioxide,  and  sand- 
stone consists  of  par- 
ticles of  sand  cemented 
together. 

Silica  is  found  in  most 
plants,  especially  in  their 
stalks  and  stems.  It 
imparts  firmness  to  the 
stems  and  to  the  resist- 
ant exterior  coating  of 
straws,  scouring  rushes, 
and  bamboo.  Sponges, 

the  quills  of  feathers,  claws  of  animals,  and  the  finger  nails 
contain  considerable  silica. 


FIG.   99.  —  INFUSORIAL   EARTH. 
MAGNIFIED. 


HIGHLY 


339.  Properties  of  Silicon  Dioxide.  —  Silica  is  harder  than 
glass;  it  is  insoluble  in  ordinary  reagents,  but  will  dis- 
solve  in    melted   alkalies.     Melted  in    the   oxyhydrogen 
flame,  quartz  can  be  drawn  into  delicate  elastic  threads, 
which  are  used  in  scientific  instruments. 

340.  Uses  of  Silicon  Dioxide.  —  White    sand,    which    is 
nearly  pure  silica,  is  used  in  making  glass  and  porcelain. 


SILICATES  321 

Common  sand  is  discolored  by  impurities,  and  if  the 
particles  are  sufficiently  irregular  and  angular  it  can  be 
used  in  sandpaper  and  mortar.  Sandstone  is  used  for 
building;  hard  varieties  are  used  for  grindstones  and 
millstones.  Ground  glass  is  glass  that  has  been  roughened 
by  blowing  sand  against  it  by  means  of  a  blast  of  air. 
Many  clear  varieties  of  quartz  are  cut  and  polished  for 
jewelry,  as  amethyst,  agate,  carnelian,  false  topaz,  and  imi- 
tation diamond.  Clear  rock  crystal  is  cut  for  lenses. 
Petrified  wood  has  been  formed  by  the  gradual  replace- 
ment of  the  woody  fiber  by  silica,  preserving  the  woody 
appearance.  Cut  and  polished  petrified  wood  is  used  as 
an  ornamental  stone.  The  fine  varieties  of  infusorial 
earth  are  used  as  abrasives  in  polishing  powders,  and  are 
also  used  in  cements,  in  refractory  fire  brick,  and  as  an 
absorbent  in  dynamite.  Quartz,  melted  by  the  oxy  hydro- 
gen flame  or  the  electric  furnace,  is  fashioned  into  tubes 
and  dishes  for  use  in  the  laboratory.  This  material  is 
called  vitrified  silica.  Silicon  dioxide  is  used  as  a  filler  in 
paint. 

341.   Silicates.  —  Silica  reacts  with  the  hydroxides  of  the 

alkali  metals,  sodium  and  potassium*  to.form  silicates  : 

tntCM;  4-£t** 
SiO2  +  2  KOH  —  >-  KjSiQg  +  H2O 


Sodium  and  potassium  silicates  are  soluble  in  water  ; 
nearly  all  the  other  silicates  are  insoluble,  stable  com- 
pounds, which  comprise  the  larger  part  of  the  earth. 
Such  minerals  as  feldspar,  mica,  hornblende,  and  clay  are 
silicates.  Various  mixtures  of  these  comprise  the  com- 
mon rocks,  as  granite,  gneiss,  and  slate. 

Sodium  and  potassium  silicates  are  made  by  heating  to 
fusion  the  metallic  hydroxides,  or  carbonates,  with  silicon 
dioxide.  The  thick  water  solution,  called  water  glass,  is 


322 


SILICON  AND  BORON 


used  in  filling  soaps,  in  making  artificial  stone  and  cement, 
in  ready  mixed  paints,  wall  coloring,  calico  printing,  and 
fireproofing  wood  and  textiles. 

Silicon  dioxide  is  the  anhydride  of  silicic  acid : 


Si02  +  H20 


H2Si03 


At  high  temperatures,  silica  combines  directly  with  basic 
oxides,  like  calcium  oxide  (§  390),  to  form  silicates  : 


SiO2  +  CaO 


CaSiO 


This  action  is  the  basis  of  the  formation  of  slag,  in  the  ex- 
traction of  iron  and  other  metals. 


342.   Glass.  —  Glass  is  a  mixture  of  silicates.     Common, 
crown,  or  window  glass  consists  of  silicates  of  sodium  and 

calcium  ;  Bohemian  glass, 
of  potassium  and  calcium 
silicates;  flint  glass  con- 
tains silicates  of  lead  or 
barium,  and  potassium. 

Glass  is  made  by  melting 
together  sand,  an  alkali, 
and  calcium  carbonate  in 
pots  of  fire  clay  (Fig.  100) 
or  tanks  made  of  fire  bricks. 


FIG.   100.  —  GLASS  FURNACE. 
a,  fire-boxes  ;  b,  melting-pots. 


The  alkali  may  be  sodium  or  potassium  carbonate  or 
a  mixture  of  these.  An  oxidizing  agent,  as  potassium 
nitrate  or  manganese  dioxide,  may  be  added  to  remove 
the  green  color  due  to  iron  compounds.  The  mixture 
is  heated  to  a  high  temperature  and  thoroughly  melted ; 
the  gases  that  are  given  off,  chiefly  carbon  dioxide,  aid  the 
mixing.  The  heating  must  continue  long  enough  to 
expel  all  of  the  gas,  or  there  will  be  bubbles  or  streaks 
in  the  finished  glass.  Any  infusible  impurities  coming  to 


GLASS  323 

the  top  are  skimmed  off.     When  the  mass  is  cooled  to 
a  pasty  condition,  it  may  be  blown  or  molded. 

Window  glass  is  made  by  the  workman  taking  a  mass  of 
the  molten  glass  on  the  end  of  a  long  iron  blowpipe,  and 
blowing  it  into  a  large  bubble.  This  is  drawn  out  into  a 
cylinder  by  swinging  it  and  rolling  it  on  a  plate.  The 
ends  of  the  cylinder  are  cut  off,  a  cut  is  made  lengthwise, 
and  the  glass  is  spread  out  flat.  Plate  glass  is  made  by 


By  courtesy  of  The  Scientific  American. 

FIG.  101.  —  ROLLING  OUT  PLATE  GLASS. 

pouring  the  molten  glass  on  a  bronze  table,  rolling  it  with 
a  hot  iron  cylinder  (Fig.  101),  and  finally  polishing  it. 
Out  glass  is  flint  glass  molded  to  the  desired  shape ;  the 
design  is  cut  by  a  wheel,  and  the  glass  polished  with 
rouge  or  putty  powder. 

Cheap  glass  dishes  and  similar  objects  are  made  by 
pressing  the  plastic  glass  in  a  die.  Bottles  are  blown  in  a 
mold.  If  the  glass  is  cooled  rapidly,  it  is  hard,  brittle, 
and  liable  to  break  under  a  shock.  To  overcome  this  it  is 


324 


SILICON  AND  BORON 


annealed,  that  is,  the  glass  is  passed  slowly  through  a  long, 
tunnel-like  furnace  from  the  hot  to  the  cooler  end,  so 
that  the  temperature  is  very  gradually  lowered.  This 
process  often  takes  several  days. 

Crown  glass  is  a  colorless  window  glass  used  for  convex 
lenses.  Bohemian  glass  is  harder  and  less  fusible,  and  is 
used  for  chemical  apparatus.  Flint  glass  is  brilliant, 
heavy,  and  soft,  and  is  used  for  concave  lenses,  lamp 
chimneys,  cut  glass,  and  for  imitation  gems,  such  as  paste 
diamonds. 

Glass  is  colored  by  dissolving  various  substances  in  the 
melted  mass.  The  green  color  of  common  glass  is  due  to 
iron  compounds  in  the  sand  and  limestone ;  chromium 
compounds  give  a  rich  green.  Compounds  of  copper  and 
cobalt  give  blue  color ;  manganese,  pink  to  violet ;  man- 
ganese with  iron,  yellow  to  brown;  silver,  yellow;  gold, 
ruby  red ;  calcium  fluoride,  white  and  translucent. 

343.  Silicon  Carbide,  or  Carborundum.  —  Silicon  carbide, 
carborundum,  is  a  crystallized  solid  varying  in  color,  and 

often  brilliant  and 
iridescent.  It  is 
extremely  hard,  and 
is  used  as  a  substi- 
tute for  emery  for 
grinding  and  pol- 
ishing in  wheels, 
hones,  and  carbo- 
rundum cloth  (Fig. 
102). 

FIG.  102.  — CARBORUNDUM  PRODUCTS.  Carborundum    is 

made  in  an  oblong 

electric  furnace,  at  the  ends  of  which  are  metal  plates  to 
which  are  attached  the  heavy  carbon  electrodes  projecting 


SILICON  CARBIDE 


325 


FIG.   103.  —  CARBORUNDUM  FURNACE  —  SECTIONAL. 

into  the  furnace  (Fig.  103).     The  electric  connection  be- 
tween the  electrodes  is  through  a  mass  of  granulated  coke. 


FIG.   104.  —  ELECTRIC  CARBORUNDUM  FURNACE. 

Sand,  a  little  salt,  and  sawdust  are  mixed  with  coke.  The 
salt  is  used  to  aid  fusion,  and  the  sawdust  to  make  the  mass 
porous.  This  mixture  is  piled  around  the  central  core  of 


326  SILICON  AND  BORON 

coke  and  held  in  place  by  side  walls  of  loosely  piled  bricks 
(Fig.  104).  The  action  in  the  furnace  is  not  electrolytic, 
but  is  due  to  the  heat  generated  through  the  resistance  of 
the  coke  to  the  current.  The  carbon  reacts  -with  the 
melted  sand  to  form  carbon  monoxide  and  carborundum : 

SiO2  +  3  C  — >•  SiC  4-  2  CO 

The  action  continues  for  about  eight  hours.  When  the 
furnace  has  cooled,  the  sides  are  torn  down  and  the  car- 
borundum removed.  The  best  crystals  are  found  around 
the  central  core.  The  crystals  are  crushed,  washed  with 
sulphuric  acid,  dried,  and  graded  according  to  size. 

344.  Silicon  fluoride,  SiF4,  is  a  colorless  gas  formed  in  the 
reaction  of  hydrofluoric  acid,   HF,  with  silica,   SiO2,  or 
with  glass.     It  decomposes  in  water,  forming  hydrofluo- 
silicic  acid,  H2SiF6,  and  silicic  acid,  H2SiO3. 

345.  Boron.  —  The  element  boron  is  of  little  importance. 
It  is  a  brown  powder,  soluble  in  many  melted  metals,  and 
infusible  at  the  temperature  of  the  electric  arc.     Its  im- 
portant compounds  are  boric  acid  and  borax. 

346.  Boric  acid,  H3BO3,  occurs  in  minute  quantities  in 
vapors  arising  from  the  earth  in  the  volcanic  regions  of 
Tuscany,  in   Italy.     Most  of  the  boric  acid  used  in  the 
United   States    is   made   by   the    reaction  of  colemanite, 
impure  calcium  borate,  with  sulphuric  acid. 

Boric  acid  is  obtained  in  fine  crystalline  scales.  It  is  a 
weak  acid,  sparingly  soluble  in  water.  It  is  used  as  an 
antiseptic  and  as  a  preservative. 

347.  Borax.  —  Sodium     tetraborate,    Na2B4O7,    is    the 
familiar  compound,  borax.     In  California  there  are  large 


BORAX  327 

deposits  of  impure  borax  and  calcium  borate,  which  supply 
this  country. 

Borax  is  obtained  from  solutions  in  large  crystals,  con- 
taining either  5  or  10  molecules  of  water  of  crystallization, 
according  to  the  temperature  at  which  they  are  deposited. 
Ordinary  borax  has  the  composition  Na2B4O7  •  10  H2O. 
A  solution  of  borax  has  a  feeble  alkaline  reaction. 

Borax  is  employed  in  large  quantities  as  an  antiseptic 
and  preservative,  and  as  a  cleansing  agent.  In  soldering 
and  welding  it  is  used  to  dissolve  the  metallic  oxides. 

348.  Borax  Bead  Tests.  —  When  heated,  crystallized  borax 
swells  during  the  evaporation  of  the  water  of  crystalliza- 
tion and  then  melts  to  a  clear  glassy  mass.  Fused  borax 
dissolves  metallic  oxides,  and  these  often  impart  to  the 
glassy  mass  a  color  characteristic  of  the  metal.  Thus, 
cobalt  compounds  give  a  blue  color,  and  manganese  com- 
pounds a  violet  color,  when  heated  with  a  drop  of  fused 
borax  in  the  oxidizing  flame. 

SUMMARY 

Silicon  is  a  very  abundant  element  which,  in  itself,  is  of  little 
practical  importance.  Silicon  dioxide  (silica)  is  its  most  common 
compound,  occurring  as  quartz  and  sand  and  as  a  constituent  of 
many  rocks. 

Silica  is  very  hard  and  fuses  only  at  high  temperatures.  It  is 
used  in  making  glass fc  mortar,  and  polishing  powders. 

Silicates  are  salts  of  silicic  acids.  Sodium  and  potassium  sili- 
cates are  soluble. 

Glass  is  a  mixture  of  silicates.  Three  varieties  are  crown,  flint, 
and  Bohemian  glass.  The  materials  are  melted  together  and 
blown  or  molded  into  shape  while  plastic.  Colors  may  be  added 
to  it  while  in  a  melted  state. 

Silicon  carbide  is  made  by  heating  coke  and  sand  in  an  electric 
furnace.  It  is  used  as  an  abrasive. 


328  SILICON  AND  BORON 

Boric  acid  is  found  in  nature,  but  much  of  it  is  made  from  cal- 
cium borate. 

Borax  occurs  in  large  deposits  in  California.  It  gives  charac- 
teristic reactions  with  metallic  oxides  used  as  bead  tests.  Borax 
is  used  in  soldering  and  welding,  and  as  a  preservative  and  cleans- 
ing agent. 

EXERCISES 

1.  Why  is  it  difficult  to  obtain  silicon  from  its  oxide  ? 

2.  Give  the  most  important  uses  of  silicon  dioxide. 

3.  Why  is  sand  the  main  final  product  of  long-continued 
disintegration  of  rock  materials  by  water  ? 

4.  What  is  water  glass  ?     How  is  it  made,  and  what  are  its 
uses? 

5.  What  is  vitrified  silica  ?     Why  should   not  basic  sub- 
stances be  melted  in  silica  ware  ? 

6.  Give  the  essential  composition  of  a  glass. 

7.  Give  the  composition  and  uses  of  the  three  chief  varie- 
ties of  glass. 

8.  Describe  the  manufacture  of  some  one  kind  of  glass. 

9.  Explain,  using  an  equation,  the  production  of   carbon 
dioxide  in  glass  making,  and  state  how  it  is  eliminated  from 
the  finished  glass. 

10.  How  is  glass  annealed  ?     What  is  the  effect  of  this  pro- 
cess on  the  properties  of  the  glass  ? 

11.  Explain,  with  the   aid  of   an  equation,  the   action    of 
hydrofluoric  acid  on  glass. 

12.  How  does  the  composition  of  hard  glass  differ  from  that 
of  soft  glass  ? 

13.  Calculate  the  percentage  of  water  of  crystallization  in 
borax. 


CHAPTER  XXVIII 

CALCIUM  AND  ITS  COMPOUNDS 

CALCIUM 

349.  Although    metallic  calcium  has  been  known  for 
many  years,  it  is  only  recently  that  it  has  been  made  in 
any  quantity.     Sir  Humphry  Davy  was  the  first  one  to 
see  the  metal,  but  failed  to  get  enough  to  determine  its 
properties.     The  credit  for  the  successful  isolation  of  cal- 
cium belongs  to  Dr.  Robert  Hare,  a  scientist  of  Philadel- 
phia.    His  electrolytic  method,  with  some  modifications, 
is  the  one  now  used  to  obtain  the  metal. 

350.  Preparation.  —  Metallic    calcium    is    prepared   by 
passing  an  electric  current  through  fused  calcium  chloride 
contained    in    a    crucible    of    graphite, 

which  acts  as  the  anode  (Fig.  105). 
At  first  the  cathode  is  an  iron  rod 
(5),  capable  of  being  raised  by  a  screw- 
mechanism  (^4).  The  calcium  deposits 
on  the  end  of  the"  iron  rod,  solidifies, 
and  grows  downward  as  an  irregular 
cylinder.  This  rod  of  calcium  becomes 
the  cathode  ((7)  as  the  iron  rod  is  FlG-  105- 

gradually  raised  out  of  the  molten  chloride  by  the  screw 
mechanism.  A  coating  of  calcium  chloride  protects  the 
calcium  from  oxidation  as  it  emerges  from  the  molten 
bath.  The  electric  current,  by  its  passage,  keeps  the 
calcium  chloride  molten  in  the  graphite  crucible,  except 

329 


330  CALCIUM  AND  ITS   COMPOUNDS 

at  the  bottom  (D),  where  it  is  kept  cold  and  is  solidified 
by  water  running  through  a  copper  coil  (EE).  The  chlo- 
ride adhering  to  the  sticks  of  calcium  is  removed  by 
hammering. 

351.  Physical  Properties.  —  Pure    calcium    is    a    silver- 
white  metal  of  brilliant  luster,  and  is  a  little  lighter  than 
magnesium.     It  is  harder  than  lead  or  tin,  but  softer  than 
zinc.     At  300°  to  400°  C.  it  is  as  soft  as  lead  and  can 
easily  be  rolled  or  hammered.     Only  a  few  metals  surpass 
calcium  as  conductors  of  electricity. 

352.  Chemical  Properties.  —  Calcium  keeps  its  luster  in 
dry  air  and  can  be  preserved  without  difficulty  in  a  stop- 
pered  bottle.     In   moist  air  its  surface  becomes  dulled. 
Molten   calcium    burns    vigorously    in    oxygen    and    in 
chlorine. 

Water  is  slowly  decomposed  by  calcium,  and  hydrogen 
is  evolved  at  a  rate  very  convenient  for  the  collection 
of  the  gas: 

Ca  +  2  H20  — ^  Ca(OH)2  +  H2 

CALCIUM  CARBONATE     C^ 

353.  Occurrence.  —  Calcium  carbonate,  CaCO3,  is  one  of 
the  most  abundant  compounds  occurring  in  nature.     In 
the  form  of  limestone  it  constitutes  whole  mountain  ranges. 
Marble,  which  exists  in  enormous  quantities  in  various 
parts  of  the  world,  is  a  purer  form  of  calcium  carbonate 
than  limestone.     Marble  was  formed  from  limestone  by 
the  action  of  heat  and  pressure  under  such  conditions  that 
carbon  dioxide,  which  generally  is  given  off  when  lime- 
stone is  heated,  was  prevented  from  making  its  escape. 

The  mineral  matter  in  shells  is  chiefly  calcium  carbon- 
ate derived  from  the  water  in  which  the  animals  lived. 


CALCIUM  CARBONATE 


331 


In  past  ages,  deposits  of  shells  became  cemented  together 
into  rock  materials.  Coquina,  or  the  loose  shell  rock  of 
Florida,  illustrates  an  early  stage  of  this  process  (Fig. 
106),  and  limestone  a  more 
complete  transformation. 

Calcite  is  a  pure  crystal- 
line form  of  calcium  carbon- 
ate, and  one  of  its  varieties, 
Iceland  spar,  gives  a  double 
refractionof  light  (Fig.  107). 
In  many  other  minerals,  such 
as  chalk  and  dolomite,  cal- 
cium carbonate  is  present.  FIG.  106.  —  COQUINA. 

354.  Properties.  —  When  pure,  calcium  carbonate  is  a 
white  solid,  often  transparent.  The  color  of  limestone 
and  many  varieties  of  marble  is  due  to  the  presence  of 
impurities.  Calcium  carbonate  occurs  naturally  in  amor- 
phous masses  and  in  crystals  of  different  forms.  When 
precipitated  from  solutions  of  calcium  salts  by  soluble 

carbonates,  it  comes  down 
at  first  as  amorphous  scales 
and  later  as  minute  crystals. 
It  is  only  very  slightly  sol- 
uble in  pure  water,  but, 
as  we  have  already  seen 
(§§  328,  329),  it  is  more 
soluble  in  water  containing 
dissolved  carbon  dioxide. 
The  hardness  of  water  in  limestone  regions  causes  it  to 
form  a  firmly  adhering  deposit  on  all  vessels  in  which  it 
is  boiled,  since  boiling  decomposes  the  calcium  bicarbonate, 
driving  off  part  of  its  carbon  dioxide  and  leaving  the  insol- 
uble carbonate.  This  deposit,  known  as  boiler  scale,  is  a 


FIG.   107.  —  ICELAND  SPAR. 


332  CALCIUM  AND  ITS   COMPOUNDS 

poor  heat  conductor,  and  clogs  the  tubes  of  steam  boilers. 
Hence  the  water  is  often  softened  before  being  introduced 
into  the  boilers. 

355  Limestone  Caves.  —  The  formation  of  underground 
caverns  in  limestone  regions  is  due  to  the  production, 
solution,  and  decomposition  of  the  bicarbonate.  Charged 


FIG.  108.  — STALACTITES  AND  STALAGMITES  IN  A  LIMESTONE  CAVE. 


with  carbon  dioxide  from  decaying  organic  materials,  the 
soil  water  dissolves  limestone  and  sinks  through  cracks  in 
the  rocks,  widening  them  as  it  goes.  Reaching  a  less 
soluble  stratum  of  rock,  it  flows  along  this,  but  dissolves 
the  limestone  above.  This  action,  continuing  for  centuries, 
finally  excavates  a  cave,  such  as  Mammoth  Cave  in  Ken- 
tucky and  Luray  Cavern  in  Virginia.  As  soon  as  these 
caves  are  hollowed  out,  a  new  process  sets  in.  The  water, 


MANUFACTURE   OF  LIME 


333 


before  it  drops  from  the  roof,  loses  some  of  its  carbon 
dioxide,  and  part  of  the  bicarbonate  is  converted  into  the 
insoluble  carbonate.  This  is  left  behind  on  the  roof  of  the 
cave.  The  drops  that  fall  to  the  floor  lose  more,  carbon 
dioxide  and  some  water  by  evaporation,  and  likewise  de- 
posit calcium  carbonate.  The  final  result  of  the  process 
is  the  formation  of  hanging  masses  of  calcium  carbonate, 
like  icicles  of  stone,  known  as  stalactites,  and  the  forma- 
tion of  round  mounds  below  called  stalagmites  (Fig.  108). 
These  in  turn  finally  unite  to  form  columns.  In  this  way 
the  cave  may  become  nearly  filled  again. 

356.  Uses  of  Calcium  Carbonate. — Natural  calcium  car- 
bonate has  three  very  important  uses.  Large  quantities 
of  limestone  and  marble  are  used  as  building  stone. 
Enormous  amounts  of  limestone  are  yearly  "  burned " 
(heated  to  expel  the  carbon  dioxide)  to  form  quicklime. 
Much  limestone  is  used  in  the  production  of  cast  iron 
(§  390).  Ground  limestone  is  frequently  used  on  farm 
land,  to  neutralize  undesirable  acids  that  may  be  present 
in  the  soil. 


CALCIUM  OXIDE 


357.  Manufacture 
of  Lime.  —  Calcium 
oxide,  or  quicklime, 
is  made  by  the  de- 
composition of  cal- 
cium carbonate  at  a 
red  heat : 
CaCOg— •»- 

CaO  +  CO2 

The  manufacture 
of  lime  is  carried  on 


FIG.  109.  —  LIME  KILN. 


334 


CALCIUM  AND  ITS   COMPOUNDS 


in  special  furnaces  called  lime  kilns 
(Fig.  109).  In  the  modern  lime 
kilns  (Fig.  110),  the  fire  is  in  side 
chambers  and  only  the  hot  gases 
find  their  way  up  through  the  charge 
of  limestone  fed  in  at  the  top  of  the 
furnace.  In  this  long  flame  process, 
the  lime  withdrawn  at  the  bottom 
of  the  kiln  is  free  from  ashes. 

If  the  limestone  contains  impuri- 
ties, as  silica,  iron,  or  alumina,  in 
any  considerable  amount,  a  poor 
quality  of  lime  is  obtained.  The 
successful  operation  of  the  kiln 
depends  upon  the  efficient  removal 
of  the  waste  gases  from  the  shaft, 
so  that  the  carbon  dioxide  which  is 
formed  does  not  cause  a  reversal  of  the  action.  This 
constitutes  a  practical  application  of  the  law  of  mass  action. 


FIG.  110.  —  LIME  KILN. 


•C — 


FIG.   111.  —  ROTARY  LIME  KILN. 

P,  gas  producer  ;  K,  kiln  ;  Z,  limestone  bin  ;  D,  dust  chamber  ;  B,  boiler  ; 
C,  cooler ;  S,  storage  bin  for  lime. 

358.   Rotary  Lime  Kiln.  —  The  best  lime  is  made  in  a 
rotary  kiln  (Fig.  Ill),  in  which  limestone,  crushed  to  one- 


QUICKLIME  335 

inch  pieces,  slowly  passes  down  the  rotating  cylinder  and 
meets  an  intensely  hot  flame  from  the  burning  of  a  blast 
of  hot  air  and  producer  gas  (or  pulverized  coal).  The 
flame  extends  a  considerable  distance  into  the  kiln,  and 
the  intense  heat  completely  expels  the  carbon  dioxide  from 
the  pieces  of  limestone  as  they  turn  over  and  over.  The 
hot  lime  at  the  lower  end  of  the  kiln  drops  into  a  rotary 
cooler.  Here  it  gives  up  its  heat  to  the  air  that  is  used 
for  the  kiln  blast. 

Heat  economy  is  not  only  secured  in  this  way,  but  also 
by  passing  the  hot  gases  from  the  top  of  the  kiln  through 
the  dust  settling  chamber  to  the  boiler,  where  these 
gases  generate  all  the  steam  necessary  for  the  gas  pro- 
ducer and  for  driving  all  the  machinery  connected  with 
the  kiln.  Few  manufacturing  processes  are  operated  with 
so  complete  utilization  of  the  heat  generated. 

The  rotary  kiln  produces  a  thoroughly  and  carefully 
burned  lime,  free  from  dust  and  ashes.  Its  small  and 
uniform  pieces  permit  compact  packing,  and  for  this 
reason  the  lime  is  less  liable  to  air-slake  than  the  larger 
lumps  of  varying  size  produced  by  other  kilns.  More- 
over, it  slakes  with  water  more  rapidly  and  evenly  than 
lime  made  by  other  processes. 

359.  Properties.  —  Pure  calcium  oxide  is  a  soft,  white, 
non-crystalline  substance  which  can  only  be  fused  and 
vaporized  at  the  temperature  of  the  electric  arc  (about 
3500°). 

It  slowly  takes  up  moisture,  forming  the  hydroxide  : 

""#aO  V  H20  — >-  Ca(OH)2 

When  water  is  put  on  lumps  of  quicklime,  cracks  soon 
appear  on  the  surface,  the  mass  swells,  and  finally  falls  to 
a  voluminous  white  powder.  The  heat  of  combination  is 


336  CALCIUM  AND  ITS   COMPOUNDS 

so  great  that  the  lime  becomes  hot,  and  clouds  of  steam 
arise.  This  energetic  action  or  process  is  called  slaking, 
and  the  product  of  the  reaction,  calcium  hydroxide,  is 
called  slaked  lime.  When  quicklime  is  left  exposed  to 
the  air,  both  water  and  carbon  dioxide  are  taken  up,  with 
the  formation  of  both  calcium  hydroxide  and  calcium  car- 

bonate.    This  process  is  known 
1  6  as  air  -slaking. 

360.  Uses.  —  On  account  of 
its  infusibility  and  dazzling  in- 
candescence in  the  oxyhydro- 
gen  flame,  the  oxide  is  used 

FIG.  1  ^.-LIME-LIGHT  BURNER.     in  the  calcium  or  lime  light.      A 

lime-light  burner   is   shown  in 

Fig.  112  ;  a  is  the  burner  tip  for  an  oxyhydrogen  flame, 
and  b  is  the  cylinder  of  quicklime.  Many  other  uses 
of  calcium  oxide  are  considered  in  connection  with  the 
hydroxide. 

CALCIUM   HYDROXIDE 

361.  Properties  and  Uses.  —  Calcium  hydroxide,  or  slaked 
lime,  is  a  soft  white  solid  when  pure,  and  is  sparingly 
soluble  in  water,  forming  a  solution  called  limewater. 
Limewater,  white  with  suspended  but  undissolved  par- 
ticles of  the  hydroxide,  is  known  as  milk  of  lime. 

When  heated,  the  hydroxide  loses  water  and  is  recon- 
verted into  the  oxide,  showing  the  reaction  to  be  a  reversi- 
ble one,  according  to  the  temperature  : 


The  water  solution  of  calcium  hydroxide  is  strongly  basic, 
a  property  which  has  led  to  the  wide  use  of  the  hydroxide 
as  a  cheap  alkali.  In  this  respect  it  stands  among  the 
bases  as  sulphuric  acid  does  among  the  acids. 


USES   OF  LIME 


337 


OUTLET 


FLOAT 
TANK 


CHEMICAL 

SUPPLY 

PIPE 


Lime,  as  a  cheap 
base,  is  used  in  the 
manufacture  of  al- 
kalies and  bleaching 
powder,  in  glass  mak- 
ing, for  whitewash, 
in  the  removal  of  hair 
from  hides,  and  in 
many  other  indus- 
tries. It  is  employed 
in  water  softening. 
In  one  process  of 
water  softening,  the 
slaked  lime  is  thor- 
oughly mixed  with 
water  in  the  chemical 
tank  (Fig.  113),  and 
then  fed  into  the  top 
of  a  long,  vertical  soft- 
ening tank.  Revolv- 
ing paddles  in  this 
tank  thoroughly  mix 
the  lime  with  the  water  to  be  softened,  and  the  following 
reaction  takes  place : 

CaH2(CO3)2  +  Ca(OH)2  — >-  2  CaCO3  +  2  H2O 

As  the  water  passes  out  of  the  bottom  of  the  softening 
tank  and  up  through  the  larger  tank  surrounding  it,  most 
of  the  calcium  carbonate  and  other  solid  impurities  settle 
out.  Any  remaining  solids  are  removed  by  the  filter,  and 
the  softened  water  flows  from  the  outlet  at  the  top.  If 
the  water  contains  permanent  hardness,  sodium  carbonate 
is  used  with  the  lime.  The  chief  use  of  lime,  however,  is 
in  the  preparation  of  mortar  and  cement. 


SLUDGE  VALVE 


FIG.  113.  —  WATER  SOFTENING  APPARATUS. 


338  CALCIUM  AND  ITS   COMPOUNDS 

362.  Mortar.  —  When  sand  is  thoroughly  mixed    with 
wet,  freshly  slaked  lime,  ordinary  mortar  is  produced. 
Mortar  is  employed  to  form  a  hard,  stony  mass,   which 
holds  together  the  stones  or  bricks  in  a  building.     The 
hardening  of  the  interior  of  rnortar  is  chiefly  due  to  the 
escape  of  water.     The  slaked  lime  forms  a  kind  of  jelly- 
like  mass  with  the  water,  in  which  the  grains  of  sand  are 
entangled.     As  the   water   evaporates,   the   calcium   hy- 
droxide sets  into  a  compact,  stony  mass,  and  the  sand 
gives  additional  strength.     At  the  outer  surface  of  the 
mortar,  which  is  exposed  to  the  air,  the  calcium  hydroxide 
reacts  with  the  carbon  dioxide  of  the  air,  forming  calcium 
carbonate : 

Ca(OH)2  +  C02— >-CaCO3  +  H2O 

This  action  takes  place  slowly,  and  forms  a  hard  protec- 
tive outer  layer,  which  prevents  water  from  again  entering 
the  mortar  and  softening  the  calcium  hydroxide.  Good 
mortar  increases  in  strength  with  age,  as  the  solidity  of 
buildings  erected  centuries  ago  shows.  Cement  is  now 
frequently  used  in  place  of  part  or  all  of  the  lime  in 
mortar. 

CALCIUM  SULPHATE 

363.  Varieties.  —  Calcium  sulphate  is,  next  to  the  car- 
bonate, the  most  abundant  and  widely  distributed  salt  of 
calcium.     It  occurs  as  the  mineral  anhydrite,  CaSO4,  and 
as  gypsum,  CaSO4  .  2  H2O.     Satinspar,  alabaster,  and  sele- 
nite  are  varieties  of  gypsum.     Selenite  is  often  found  in 
large,    transparent   crystals,    so   soft    that    they    can    be 
scratched  with  the  finger  nail.     Gypsum  is  used  for  the 
same  purpose  as  limestone  in  improving  soils. 

364.  Plaster  of  Paris.  —Gypsum  is  but  sparingly  soluble 
in  water;  its  solubility  increases  to  40°  and  then  decreases. 


CALCIUM  PHOSPHATES  339 

When  heated  to  the  proper  temperature,  gypsum  loses 
three  quarters  of  its  water  of  crystallization,  and  the 
residue  may  be  said  to  have  one  molecule  of  water  of 
crystallization  to  every  two  molecules  of  calcium  sulphate, 
(CaSO4)2  •  H2O.  The  chalky  powder  resulting  from  the 
heating  is  known  as  plaster  of  Paris.  On  a  large  scale  it 
is  made  by  heating  in  kilns  a  charge  of  gypsum  broken 
into  small  lumps  to  insure  evenness  in  "burning."  Care 
is  taken  not  to  overheat;  125°  C.  is  the  most  favorable 
temperature  for  the  process. 

365.  Plaster  Casts.  —  When   plaster    of    Paris    is    wet, 
water  is  again  taken  up,  forming  needles  of  crystallized 
gypsum  which,  becoming  entangled,  set  or  form  a  hard 
mass.     The  hardening  is  also  accompanied  by  a  slight  in- 
crease in    volume.     This   property   explains   the   use   of 
plaster  of  Paris  in  making  casts.     The  slight  expansion 
secures  a  sharp  impression  of  the  mold.     The  powder  is 
mixed  with  about  a  third  its  weight  of  water,  the  pasty 
mass  put  into  the  mold,  and  in  less  than  half  an  hour  the 
plaster  sets.     The  ivory  surface  of  casts  is   secured   by 
dipping  them  in  melted  paraffin  or  by  painting  them  with 
a  solution  of  paraffin  in  petroleum  ether.     The  solvent  in 
the  latter  case  evaporates,  leaving  the  waxy  filling  in  the 
pores  of  the  cast  and  making  it  impervious   to   water. 
Many  beautiful  ornamental  objects  are  now  made  by  plat- 
ing a  thin  film  of  metal  on  a  plaster  of  Paris  base.     Plaster 
of  Paris  is  also  used  for  rigid  bandages  in  surgery  and  as 
a  surface  coating  for  walls.     Stucco  is  plaster  of  Paris  and 
rubble,  mixed  with  sizing  or  glue  instead  of  water. 

366.  Calcium  Phosphates.  —  The  phosphates  of  calcium 
are   of   great   importance  to  organic   life.     The   mineral 
matter  in  bones  of  animals  is  essentially  normal  calcium 


340  CALCIUM  AND  ITS   COMPOUNDS 

phosphate,  Ca3(PO4)2.  This  compound  occurs  as  phos- 
phorite, which  has  been  derived  from  animal  remains. 
G-uano  contains  phosphates  in  addition  to  nitrogenous 
compounds.  Phosphates  are  an  important  plant  food,  but 
to  be  available  must  be  in  a  soluble  form  that  can  be 
taken  up  by  the  plants.  The  soluble  phosphates  result 
from  the  decomposition  of  rocks  containing  phosphates. 
Since  the  process  is  a  slow  one,  the  supply  of  soluble 
phosphates  in  cultivated  soils  often  becomes  scanty.  To 
supply  this  need,  the  manufacture  of  soluble  phosphates 
for  fertilizers  has  grown  to  be  an  important  industry. 

The  monocalcium  phosphate,  or  superphosphate  of  lime, 
CaH4(PO4)2  •  2  H2O,  is  the  most  important  artificial  ferti- 
lizer. It  is  made  by  treating  rock  phosphates  with  crude 
sulphuric  acid.  The  superphosphate  formed  is  readily 
soluble  in  water,  and  when  spread  upon  the  soil  is  available 
for  plant  use.  The  superphosphate  is  also  used  in  baking 
powders. 

367  Bleaching  Powder.  —  Bleaching  powder,  or  chloride 
of  lime,  is  made  by  passing  chlorine  over  freshly  slaked 

lime  spread  on  the  floors  of 
a  series  of  absorption  cham- 
bers (Fig.  114).  Chemists 


FIG.  114.  are  still  in  doubt  as  to  the 

reactions  involved  in  the 

process  and  the  formula  of  the  product.  The  latter, 
however,  is  often  represented  as  CaOCl2. 

Bleaching  powder  is  an  unstable  white  powder  which 
is  slightly  soluble  in  water.  When  bleaching  powder  is 
treated  with  acids,  chlorine  is  evolved.  Hence  the  pow- 
der is  used  as  a  source  of  chlorine  for  bleaching  purposes. 

The  cotton  to  be  bleached  is  freed  from  grease  and 
oil.  The  cloth  is  next  soaked  in  a  solution  of  bleaching 


SUMMARY  341 

powder,  then  dipped  in  dilute  acid,  and  finally  thoroughly 
washed  to  remove  the  chemicals  (cf.  §  80).  The  solu- 
tions used  are  very  weak,  to  prevent  injury  to  the  fiber 
of  the  cloth. 

When  exposed  to  the  air,  bleaching  powder  slowly  reacts 
with  the  carbonic  acid  formed  by  the  union  of  carbon  di- 
oxide with  water.  As  a  result  chlorine  is  liberated,  and 
for  this  reason  the  powder,  often  called  chloride  of  lime,  is 
used  as  a  disinfectant  and  germicide. 

SUMMARY 

Calcium,  although  very  abundant  in  nature,  is  rarely  seen  as 
metal. 

It  can  be  obtained  by  the  electrolysis  of  fused  calcium  chloride. 
The  most  important  calcium  compounds  are : 
the  carbonate  (limestone,  chalk,  marble)  ; 
the  hydroxide  (slaked  lime)  ; 
the  oxide  (quicklime)  ; 
the  phosphate  (phosphorite) ; 
the  sulphate  (gypsum). 

Lime  is  made  by  heating  calcium  carbonate.  Slaked  lime  is 
made  by  adding  water  to  quicklime.  Air-slaked  lime  is  a  mixture 
of  calcium  hydroxide  and  calcium  carbonate,  formed  by  the  ex- 
posure of  quicklime  to  air. 

Slaked  lime  is  used  in  making  mortar,  which  hardens  by  the 
evaporation  of  water  -and  the  absorption  of  carbon  dioxide. 

Plaster  of  Paris  is  made  by  partly  dehydrating  gypsum.  It  is 
used  in  making  plaster  casts. 

Calcium  phosphates,  derived  from  bone  ash  and  rock  deposits 
are  used  in  making  fertilizers. 

Bleaching  powder  is  made  by  passing  chlorine  over  slaked  lime 
It  is  used  in  bleaching  and  as  a  disinfectant. 


342  CALCIUM  AND  ITS   COMPOUNDS 

EXFRCISES 

1.  Write  the  equation  for  the  reaction  between  water  and  (a) 
sodium,  (&)  calcium.    How  do  the  reactions  differ  in  intensity?  /^ 

2.  What  is  the  "  fur  "  deposited  in  tea  kettles  in  which  hard 
water  is  boiled  ? 

3.  Explain  the  formation  of  stalactites  and  stalagmites. 

./      4.   How  much  quicklime  can  be  obtained  from  4  tons  of 
limestone  containing  98  %  of  calcium  carbonate  ? 

5.  Why  is  the  production  of  lime  hastened  by  blowing  air 
or  steam  into  a  lime  kiln  ? 

6.  In  the  laboratory,  loosely  stoppered  bottles  that  contain 
quicklime   are   sometimes  found  with   the  sides   broken  out. 
How  do  you  account  for  this  ? 

7.  Write  the  equations  that  illustrate  the  formation  of  air- 
slaked  lime. 

8.  What  weight  of  water  enters  into  combination  in  slaking 
'  500  Ib.  of  quicklime  ? 

9.  Lime  water  standing  exposed  to  air  becomes  coated  with 
a  film  of  insoluble  substance.     What  is  the  substance  ?     Ex- 
plain its  formation. 

10.   How  could  quicklime  be  made  from  slaked  lime  ? 
'Y/    11.   What  weight  of  nitric  acid  would  be  required  to  neu- 
tralize 35  grams  of  calcium  hydroxide  ? 

12.  Compare  the  hardening  of  mortar  with  that  of  plaster 
of  Paris. 

13.  For  what  reason  is  normal  calcium  phosphate  converted 
into  "  superphosphate  "  in  the  manufacture  of  fertilizers  ? 

14.  Why  is  bleaching  powder  shipped  in  air-tight  containers  ? 

15.  Account  for  the  disinfecting  power  of  "  chloride  of  lime." 
/  16.   Calculate  the  weight  of  quicklime  that  one  might  ex- 
pect to  get  from   1000  kilograms  of  pure  limestone.     What 
weight  of  carbon  dioxide  would  be  given  off  during  the  action  ? 
What  volume  would  the  gas  have,  standard  conditions  ? 


CHAPTER   XXIX 
MAGNESIUM,  ZINC,  AND  MERCURY 

MAGNESIUM 

368.  Occurrence  and  Preparation.  —  Although  magnesium 
is  of  comparatively  little  commercial  importance,  its  com- 
pounds are  very  abundant  in  nature.     The  most  impor- 
tant of  these  are  dolomite,  a  double  carbonate  of  calcium 
and  magnesium  (CaCO3  •  MgCO3);  magnetite  (MgCO3); 
carnallite,  a  double  chloride  of  potassium  and  magnesium 
(KC1  •  MgCl2  •  6  H2O) ;  kainite,  a  double  salt  of  potassium 
chloride  and  magnesium  sulphate  (KC1  •  MgSO4  •  3  H2O). 
Magnesium  is  also  found  in  combination  with  other  ele- 
ments  in   various   natural   silicates,   for   example,  horn- 
blende and  asbestos.     Epsom  salts,  magnesium   sulphate 
(MgSO4  •  7  H2O),  is  found  in  some  springs  whose  waters 
owe  their  laxative  properties  to  its  presence. 

The  metal  is  commercially  obtained  by  the  electrolysis 
of  carnallite.  The  salt  is  fused,  together  with  some  com- 
mon salt  or  cryolite,  in  an  iron  crucible  which  acts  as  the 
cathode.  A  carbon  rod  serves  as  the  anode. 

369.  Properties  and  Uses.  —  Magnesium  is  a  silvery  white 
metal  of  low  specific  gravity.     It  resembles  both  calcium 
and  zinc  in  its  properties,  and  stands  between  them  in  me- 
tallic character.     It  decomposes  water  slowly  at  100°,  but 
does  not  affect  it  at  ordinary  temperatures.     Moist   air 
acts  on  magnesium  slowly,  forming  a  basic  carbonate  of 
magnesium.     Magnesium  burns   with   comparative   ease, 

343 


344  MAGNESIUM,   ZINC,  AND  MERCURY 

with   the   evolution   of   a   brilliant  white   light  of  great 
actinic  power.     The  oxide  is  formed  by  this  reaction: 


Dilute  acids  react  with  magnesium  very  readily,  hy- 
drogen usually  being  evolved. 

Magnesium  is  one  of  the  few  elements  that  enter 
into  direct  combination  with  nitrogen.  When  nitrogen 
is  passed  over  red-hot  magnesium,  magnesium  nitride, 
Mg3N2,  is  formed. 

Magnesium  is  sometimes  used  in  flashlight  preparations 
for  photographic  purposes  because  of  the  actinic  power  of 
the  light  it  gives  in  burning.  It  is  also  used  in  making 
fireworks,  and  certain  light  alloys. 

370.  Compounds  of  Magnesium.  —  The  common  salts  of 
magnesium  are  stable  substances  and,  with  the  exceptions 
of  the  carbonate  and  the  phosphate,  are  soluble  in  water. 
The  formulas  of  the  magnesium  compounds  show  that  the 
element  has  a  valence  of  two,  or  we  may  say  it  forms 
bivalent  ions. 

Mixtures  of  magnesium  carbonate  with  magnesium 
hydroxide  are  used  in  pharmaceutical  preparations  and  in 
face  powders. 

The  acetate,  bromide,  citrate,  and  sulphate  of  magnesium 
are  valued  on  account  of  their  medicinal  properties.  The 
sulphate  is  the  medicinal  constituent  of  many  commercial 
laxative  waters.  Magnesium  chloride  is  used  to  some 
extent  for  fireproofing  materials  and  in  the  manufacture 
of  disinfectants. 

Many  magnesium  compounds,  when  heated  in  an 
oxidizing  flame,  are  converted  into  magnesium  oxide. 
This,  when  moistened  with  a  solution  of  cobalt  nitrate 
and  heated,  yields  a  mass  having  a  pale  pink  color. 


EXTRACTION  OF  ZINC 


345 


ZINC 

371.  Minerals  are  the- elements  and  compounds  whose 
mixtures  make  up  the  inorganic  material  of  the  earth. 
Copper,  sulphur,  rock  salt  (NaCl),  silica  (SiO2),  calcite 
(CaCO3),  and  hematite  (Fe2O3)  are  examples  of  minerals. 

372.  Ores  are  the  natural  deposits  from  which  elements, 
especially  the  metals,  are  extracted.      An  ore  is  seldom 
composed  of  a  single  mineral. 


FIG.  115. 

373.  Extraction  from  Ores.  —  Zinc  is  not  found  in  the 
uncombined  state.  Some  of  its  common  ores  are  zinc 
blende,  ZnS;  smithsonite,  ZnCO3;  zincite,  ZnO. 

To  separate  zinc  from  the  oxide,  the  ore  is  finely  pow- 
dered and  mixed  with  coal.  The  mixture  is  then  heated 
in  earthenware  retorts  (Fig.  115,  a).  The  carbon  reduces 
the  zinc  oxide: 

ZnO  +  C  — >-  Zn  +  CO 


346  MAGNESIUM,   ZINC,  AND  MERCURY 

The  temperature  in  the  process  is  raised  above  the  boiling 
point  of  the  metal,  950°,  which  therefore  passes  off  as  a 
gas,  and  is  condensed  in  earthenware  or  iron  receivers  (J). 
When  the  ore  is  not  an  oxide,  a  preliminary  operation 
must  precede  the  reduction.  This  consists  in  heating 
the  ore  on  grates  in  contact  with  air.  The  operation  is 
known  as  roasting,  and  converts  the  metal  into  an  oxide. 
In  the  case  of  zinc  sulphide,  care  is  taken  not  to  convert 
it  into  the  sulphate. 

ZnCO3  — >-  ZnO  +  CO2 
2  ZnS  +  3  O2  — >-  2  ZnO  +  2  SO2 

The  oxide  that  results  in  these  reactions  is  then  reduced 
with  the  carbon  in  the  manner  that  has  been  described. 
The  silicate  is  reduced  directly. 

Zinc,  as  extracted  from  its  ores,  usually  contains  carbon, 
arsenic,  cadmium,  and  other  impurities.  It  is  freed  from 
these  by  distillation. 

374.  Physical  Properties.  —  Zinc  is  bluish  white  in  color. 
It  comes  into  the  market  in  the  form  of  heavy  bars, 
called  ingots  or  spelter,  formed  by  pouring  the  melted 
metal  into  molds.  In  this  form,  the  metal  is  crystalline 
in  structure  and  rather  brittle.  Between  100°  and  150°  C. 
it  is  malleable  and  ductile,  and  can  be  rolled  into  sheets. 
After  having  been  obtained  in  this  form,  it  remains 
malleable  at  ordinary  temperatures.  At  300°  it  again 
becomes  brittle  and  can  be  powdered. 

Granulated  or  mossy  zinc  is  a  form  much  used  in  the 
laboratory.  It  is  made  by  pouring  the  melted  metal 
into  water.  Zinc  dust  is  obtained  by  the  distillation  of 
the  metal.  As  long  as  the  receiver  remains  comparatively 
cold,  the  distilled  zinc  collects  in  the  form  of  a  powder. 
This  operation  is  similar  to  the  one  by  which  sulphur  is 


CHEMICAL  PROPERTIES   OF  ZINC  347 

obtained  as  flowers  of  sulphur.     Zinc  dust  always  contains 
a  certain  amount  of  the  oxide. 

375.  Chemical  Properties.  —  Zinc  is  regarded  as  distinctly 
metallic,  but  it  differs  considerably  from  such  metals 
as  calcium  and  sodium.  It  resembles  magnesium  more 
closely.  Zinc  does  not  act  on  water  at  ordinary  tem- 
peratures. Air  attacks  it  slowly  in  the  presence  of  mois- 
ture, forming  a  basic  carbonate,  which  acts  as  a  protective 
coating,  so  that  only  the  outer  layer  of  the  metal  is 
affected.  When  zinc  is  heated  in  air  or  oxygen,  it  burns 
with  a  bluish  flame,  forming  zinc  oxide: 

2Zn  +  O2  —  ^2ZnO 

Zinc  reacts  readily  with  dilute  acids,  forming  zinc  salts, 
and,  as  a  rule,  liberates  hydrogen  : 


Zn  +  2HCl— 
Zn  +  H2SO4  —  >-  ZnSO4  +  H2 

In  acting  on  zinc  (or  other  metals)  nitric  acid  and  con- 
centrated sulphuric  acid  do  not  liberate  hydrogen,  since 
they  act  as  oxidizing  agents  and  convert  the  hydrogen 
into  water.  In  these  cases,  the  gases  that  are  given  off 
are  reduction  products  of  the  acids. 

The  action  of  dilute  acids  on  zinc  is  hastened  by  the 
presence  of  certain  solid  substances  in  contact  with  the 
metal.  Pure  zinc  will  scarcely  react  with  acids,  but  if 
it  is  impure,  solution  takes  place  with  great  rapidity.  A 
similar  effect  is  produced  by  the  presence  of  a  very  small 
amount  of  copper,  or  other  metal,  as  a  deposit  on  the  sur- 
face of  the  zinc.  In  these  cases  the  particles  of  carbon 
or  copper  act  like  cathode  plates  of  a  voltaic  cell.  Hence 
the  velocity  of  the  evolution  of  hydrogen  from  acids  is 
increased  by  their  presence. 


348  MAGNESIUM,  ZINC,  AND  MERCURY 

Zinc  reacts  with  solutions  of  potassium  hydroxide  to 
form  potassium  zincate  and  hydrogen  : 

Zn  +  2  KOH  — -*•  K2ZnO2  +  H2 

When  hydrochloric  acid  is  added  to  potassium  zincate, 
zinc  hydroxide  is  first  formed  and  then  reacts  with  an 
excess  of  hydrochloric  acid  to  form  zinc  chloride. 

Many  compounds  of  zinc,  when  heated  on  charcoal  or  on 
a  plaster  of  Paris  block  before  a  blowpipe,  yield  zinc  oxide, 
yellow  when  hot,  and  white  when  cold.  If  the  oxide  is 
moistened  with  a  drop  of  a  solution  of  cobalt  nitrate,  and 
again  heated,  a  bright  green  mass  containing  a  compound 
of  zinc  and  cobalt  oxides  is  obtained. 

376.  Uses.  —  Zinc  is  used  in  making  several  important 
alloys.     Brass  is  composed  of  copper  and  zinc  ;    German 
silver  contains  copper,  zinc,  and  nickel  ;  bronze  sometimes 
contains  zinc  in  addition  to  copper  and  tin. 

Galvanized  iron  is  iron  covered  with  a  thin  layer  of 
zinc,  which  acts  as  a  protective  coating  and  prevents 
rusting.  The  old  process  for  galvanizing  consists  of 
thoroughly  cleaning  the  iron  by  immersing  (pickling)  it 
in  an  acid  solution  to  remove  rust,  treating  it  with  some 
other  cleaning  solution,  and  then  dipping  it  into  molten 
zinc.  The  zinc  forms  an  alloy  with  the  surface  of  the 
iron.  A  more  recent  process  for  galvanizing  consists  in 
plating  the  iron  with  zinc.  The  electrolytic  bath  generally 
consists  of  a  solution  of  either  zinc  sulphate,  or  zinc  sul- 
phate mixed  with  other  salts.  Another  use  of  zinc  is  for 
the  anode  plates  of  batteries. 

377.  Zinc  Oxide  and  Hydroxide.  —  Zinc  oxide,  ZnO,  is 
much  used  as  a  white  pigment  for  paints.     It  does  not 
have  as  great  covering  power  as  white  lead,  but  it  has  the 


SALTS  OF  ZINC  349 

advantage  of  not  turning  black  from  contact  with  hydrogen 
sulphide.  It  can  be  made  by  burning  zinc  or  by  heating 
zinc  hydroxide  or  zinc  carbonate  : 

Zn(OH)2  (heated)  — >-  ZnO  +  H2O 
ZnCO3       (heated)  — >-  ZnO  +  CO2 

A  mixture  of  zinc  oxide  and  white  lead  is  considered 
preferable  to  the  use  of  either  alone,  as  zinc  oxide  scales, 
while  white  lead  powders  or  chalks  on  being  exposed  to 
the  weather.  In  paints  containing  a  mixture  of  zinc 
oxide  and  white  lead,  these  two  tendencies  counteract  each 
other  to  some  extent  and  the  paint  is  made  more  durable. 
On  adding  potassium  hydroxide  to  a  solution  of  a  zinc 
salt,  zinc  hydroxide  is  precipitated,  since  this  substance  is 
insoluble  in  water.  If  an  excess  of  potassium  hydroxide 
is  added,  the  hydroxide  is  dissolved,  forming  potassium 

zincate  : 

ZnCl2  +  2  KOH  — ->-  2  KC1  +  Zn(OH)2 

Zn(OH)2  +  2  KOH  — +-  K2ZnO2  +  2  H2O 

378.  Salts  of  Zinc.  —  Zinc  chloride,  ZnCl2,  is  obtained 
by  the  action  of  hydrochloric  acid  and  zinc.  It  is  an 
extremely  deliquescent  substance,  sometimes  used  as  a 
drying  agent.  It  also  has  the  power  to  dissolve  metallic 
oxides  ;  because  of  this  property  its  solutions  make  good 
soldering  fluids  for  metals.  Wood  that  has  been  soaked 
in  a  solution  of  zinc  chloride  resists  decay.  Zinc  chloride 
is  also  used  as  a  solvent  for  cellulose. 

Zinc  sulphate,  ZnSO4,  is  used  in  making  battery  solutions. 

Zinc  sulphide,  ZnS,  found  in  nature  as  zinc  blende,  can 
be  prepared  by  the  direct  combination  of  zinc  dust  and 
sulphur,  or  it  can  be  precipitated  from  solutions  of  zinc  salts 
by  the  addition  of  hydrogen  sulphide  : 

ZnCl2  +  H2S  — >-  ZnS  +  2  HC1 


350  MAGNESIUM,   ZINC,  AND  MERCURY 

But  this  reaction  is  reversible  ;  that  is,  zinc  sulphide  will 
dissolve  in  dilute  hydrochloric  acid  with  the  formation  oi 
zinc  chloride  and  hydrogen  sulphide  : 

ZnS  +  2  HC1  — >•  ZnCl2  +  H2S 

For  this  reason,  the  reaction  shown  in  the  first  equation  is 
never  complete  ;  for  when  a  certain  amount  of  hydrochloric 
acid  has  been  formed,  the  second  reaction  begins  to  take 
place.  This  condition  is  a  good  illustration  of  the  opera- 
tion of  the  law  of  mass  action  (§  168).  Hydrogen  sul- 
phide is  only  slightly  ionized,  but  its  ions  are  necessary  for 
the  first  reaction.  If,  however,  a  strong  acid  is  present, 
its  hydrogen  ions  increase  the  total  concentration  of  the 
hydrogen  ions  to  such  an  extent  that  the  dissociation  of 
the  hydrogen  sulphide  is  greatly  lessened.  Hence  the 
number  of  sulphur  ions  becomes  very  small,  and  there  is 
but  little  tendency  to  form  the  sulphide.  If  we  dispose 
of  the  hydrogen  ions  as  fast  as  they  are  formed,  by 
adding  such  a  substance  as  ammonium  hydroxide,  the  pre- 
cipitation of  the  zinc  sulphide  will  be  complete.  If,  on 
the  other  hand,  much  acid  is  present  in  the  solution,  the 
precipitation  will  be  entirely  prevented. 
All  soluble  zinc  salts  are  poisonous. 

MERCURY 

379.  Occurrence  and  Separation.  —  Mercury  is  found  only 
in  a  few  localities,  the  deposits  of  Spain,  Italy,  Austria- 
Hungary,  and  the  United  States  being  the  more  important. 
The  chief  ore  of  mercury  is  cinnabar,  HgS.  Mercury  is 
obtained  from  cinnabar  by  heating  in  contact  with  air 
(roasting)  in  order  to  convert  the  sulphur  into  sulphur 
dioxide  and  to  vaporize  the  mercury : 

HgS  +  02  — >-  Hg  +  S02 


PROPERTIES   OF  MERCURY  351 

The  crude  mercury  vapor  thus  obtained  is  condensed  and 

purified. 

380.  Physical  Properties.  —  At    ordinary   temperatures, 
mercury,  commonly   known   as  quicksilver,  is  a   silvery- 
white  liquid,  with  a  brilliant  metallic  luster.     Its  density 
is  greater  thaa  that  of  lead,  so  that  iron  easily  floats  on  it. 
Mercury  solidifies  to  a  substance  resembling  tin  at  about 
—  40°  C,  and  boils  at  a  temperature  below  red  heat,  but 
vaporizes  slowly  at  ordinary  temperatures.     It  is  a  good 
conductor  of  electricity.     The  molecular  weight  of  mer- 
cury, as  found  from  its  vapor  density,  is  the  same  as  the 
atomic  weight,  200 ;  hence  there  is  one  atom  in  the  mole- 
cule of  mercury  vapor. 

The  vapor  of  mercury  is  highly  poisonous,  as  is  the 
metal  itself  when  finely  divided.  Mercury  can  be  ob- 
tained as  a  fine  gray  powder  by  shaking  it  violently  with 
flour,  grease,  or  any  substance  that  will  coat  the  minute 
drops  and  prevent  them  from  uniting  to  form  a  fluid  mass. 
This  process,  known  as  extinguishing,  is  used  in  the  prepa- 
ration of  blue  pills  and  mercurial  ointments. 

381.  Amalgams.  —  Mercury  has  the  power  of  dissolving 
many  other  metals,  forming  alloys  with  them  called  amal- 
gams.    Mercury  dropped  on  a  gold  ring  will  whiten  it  by 
amalgamating  with  the  gold.      These  amalgams  are  not 
true   compounds,    as   they  have   a   varying   composition. 
When  there  is  a  large  excess  of  mercury,  amalgams  are 
liquid ;  otherwise  they  are  solid. 

382.  Chemical  Properties.  —  Mercury   combines    readily 
with  the  halogens  and  sulphur.     Oxygen  does  not  com- 
bine with  it  at  ordinary  temperatures,  but  at  high  temper- 
atures it  forms  oxides,  which  at  still  higher  temperatures 


352  MAGNESIUM,   ZINC,   AND  MERCURY 

dissociate  into  mercury  and  oxygen.     This  is  shown  by 
the  reversible  equation : 

2  Hg  +  02  ^±  2  HgO 

Pure  dilute  acids  do  not  attack  mercury.  Concentrated 
nitric  acid  dissolves  it  readily,  and  dilute  nitric  acid  also 
attacks  it  in  the  presence  of  nitrogen  peroxide.  Zinc  and 
copper  displace  mercury  from  solutions  of  its  salts  and 
furnish  a  simple  means  of  testing  for  a  soluble  salt  of 
mercury. 

383.  Uses.  —  Mercury   is  used   in    important   scientific 
instruments,    such  as  the    thermometer    and    barometer. 
It  is  also  used  for  the  collection  of  gases  soluble  in  water. 
Its  most  important  uses,  however,  are  in  the  various  amal- 
gams.    Amalgams  of  silver  and  other  metals  are  used  in 
filling  teeth.     Gold  and  silver  are  extracted  by  allowing 
the  crushed  ore  to  flow  in  a  thin  mud  over  tables  covered 
with  mercury.     The  gold  amalgamates  with  the  mercury, 
from  which  it  can  be  separated  by  distilling  the  mercury. 

Other  uses  of  mercury  and  its  compounds  are  in  the 
manufacture  of  fulminates  for  explosive  caps,  in  electrical 
appliances,  and  in  the  preparation  of  paints. 

COMPOUNDS   OF  MERCURY 

Mercury  forms  two  series  of  compounds,  the  mercurous 
and  the  mercuric.  The  chlorides  are  the  most  important 
salts,  and  may  be  taken  as  typical  of  the  two  series. 

384.  Mercurous  Chloride,  known  as  calomel,  has  its  com- 
position represented  by  the  formula  HgCl.     Since  it  is  in- 
soluble in  water,  it  maybe  prepared  by  treating  a  solution 
of  a  mercurous  compound  with  a  chloride.     It  is  produced 


COMPOUNDS   OF  MERCURY  353 

commercially  by  heating  a  mixture  of  mercuric  chloride 
and  mercury: 

HgCl2  +  Hg  — »-  2  HgCl 

Mercurous  chloride  is  a  white  powder.  Exposed  to  the 
light,  it  slowly  blackens  on  account  of  the  liberation  of  mer- 
cury by  the  reversal  of  the  above  reaction.  It  is  extensively 
used  in  medicine. 

385.  Mercuric  Chloride.  — The  common  names  of  mercu- 
ric chloride  are  corrosive  sublimate  and  bichloride  of  mer- 
cury.    Its  formula  is  HgCl2.     Mercuric  chloride  is  made 
by  heating  a  mixture  of  sodium  chloride  and  mercuric  sul- 
phate ;  the  chloride  sublimes,  as  its  name  indicates.     The 
sublimate  is  a  white,  translucent  mass,  from  which  the 
salt  can  be  obtained  in  silky   needles  by  dissolving  in 
water  and  recrystallizing.     It  is  slightly  soluble  in  water 
at  ordinary  temperatures,  but  at  higher  temperatures  it  is 
more  soluble.      Corrosive  sublimate  is  a  violent  poison.     It 
is  also  a  powerful  antiseptic  and  germicide.    For  this  pur- 
pose, very  dilute  solutions  are  used  (1  part  to  1000  parts 
of  water).     With  the  alkaline  chlorides  it  forms  double 
salts  more  soluble  than  mercuric  chloride  by  itself,  and 
much  used  in  making  antiseptic  solutions. 

386.  Other  Compounds.  —  The  nitrates   of  mercury  are 
the  soluble  mercury  compounds  most  frequently  met  in 
the  laboratory.     Mercuric  oxide  is  used  in  the  prepara- 
tion of  paints  for  ship  bottoms.     These  paints  are  suffi- 
ciently poisonous  to  prevent  the  fouling  of  the  bottom  by 
marine  growths.     Mercuric  sulphide  forms  when  hydrogen 
sulphide  is  added  to  a  solution  of  either  a  mercurous  or  a 
mercuric  salt.     If  mercurous  sulphide  is  first  formed,  it 
decomposes  into  a  mixture  of  mercuric  sulphide  and  mer- 
cury.    Vermilion  is  mercuric  sulphide. 


354  MAGNESIUM,   ZINC,   AND  MERCURY 

MAGNESIUM 
SUMMARY 

Atomic  weight  24.     Valence  2. 

Magnesium  is  of  little  commercial  importance.     It  is  used  in 
making  several  light  alloys,  in  fireworks,  and  in  flashlight  powders. 

When  heated,  magnesium  combines  directly  with  nitrogen. 

Common  magnesium  salts,  with  the  exceptions  of  the  carbonate 
and  phosphate,  are  soluble  in  water. 

Several  magnesium  salts  are  used  in  medicine. 

The  carbonate  and  the  hydroxide  are  used  in  face  powders  and 
in  the  manufacture  of  other  pharmaceutical  preparations. 

Magnesium  chloride  is  used  for  fireproof  ing  materials. 

Epsom  salts  is  crystallized  magnesium  sulphate,  MgSO4  •  7  H  2O. 

EXERCISES 

1.  For  what  is  magnesium  used  ? 

2.  Magnesium   oxide  is  slightly  soluble  in  water.      Would 
the  solution  give  an  alkaline  or  an  acid  reaction  ?     Why  ? 

3.  What  reaction  takes  place  when  dilute  sulphuric  acid  is 
added  to  magnesium  ? 

4.  Mention  two  ways  by  which  carbon  dioxide  could  be  ob- 
tained from  magnesite. 

5.  What  is  Epsom  salts  ? 

6.  How  many  grams  of  magnesia,  MgO,  could  be  prepared 
by  heating  20  grams  of  magnesium  carbonate  ?     How  many 
liters  of  carbon  dioxide  would  be  liberated  ? 

7.  When  0.362  gram  of  magnesium  was  added  to  an  excess 
of  dilute  hydrochloric  acid,  365  c.c.  of  hydrogen  was  liberated. 
At  the  time  the  measurement  was  made,  the  temperature  was 
21°  C.  and  the  pressure  was  770  mm.     From  the  data  given  cal- 
culate the  hydrogen  equivalent  of  inaguesium. 


EXERCISES  355 

ZINC 

SUMMARY 

Atomic  weight  65.  Valence  2.  Melting  point  419°.  Boiling 
point  918°. 

A  mineral  is  an  inorganic  element  or  compound  found  native  in 
the  earth. 

An  ore  is  a  substance  that  is  mined  because  it  contains  a  min- 
eral from  which  some  useful  element,  generally  a  metal,  can  be 
extracted. 

Zinc  is  usually  obtained  by  roasting  the  ore,  to  produce  zinc 
oxide,  and  then  reducing  the  oxide. 

Spelter,  sheet  zinc,  granulated  or  mossy  zinc,  and  zinc  dust 
are  commercial  forms  of  zinc. 

Brass  and  German  silver  are  common  alloys  of  zinc. 

Zinc  is  a  dualistic  element,  since  it  acts  like  a  metal  with  acids 
and  like  a  non-metal  with  strong  bases. 

Zinc  hydroxide  acts  as  a  base  in  the  presence  of  strong  acids 
and  as  an  acid  in  the  presence  of  strong  bases. 

Zinc  oxide  is  used  in  the  preparation  of  zinc  ointment ;  it  is  also 
used  as  a  substitute  for  white  lead  as  a  paint  pigment. 

Zinc  chloride  is  used  to  clean  metals  preparatory  to  soldering ; 
as  a  wood  preservative  ;  as  a  solvent  for  cellulose. 

Zinc  sulphide  is  white. 

Zinc  sulphate  is  used  in  the  preparation  of  battery  fluids  and  in 
the  manufacture  of  fireproof  paints. 

EXERCISES 

1.  Starting  with  zinc  carbonate,  describe  the  preparation  of 
four  commercial  forms  of  zinc. 

2.  Name  two  alloys  of  zinc  and  tell  what  each  contains. 

3.  What  is  galvanized  iron  ? 


356  MAGNESIUM,  ZINC,   AND  MERCURY 

4.  Why  does  zinc  corrode  very  slowly  in  air  ? 

5.  What  advantage  is  there  in  using  zinc  oxide  (zinc  white) 
in  place  of  white  lead  for  a  paint  pigment  ? 

6.  Name  a  compound  that  would  form,  zinc  hydroxide  on 
the  addition  of  the  right  amount  of  hydrochloric  acid. 

7.  Write  equations  showing  how  hydrogen  could  be  pro- 
duced by  the  reaction  of  either  an  acid  or  a  base  with  zinc. 

8.  Why  is  wood  sometimes  impregnated  with  a  solution  of 
zinc  chloride  ?  \ 

9.  Why  is  tin  plate,  preparatory  to  soldering,  often  wet' 
with  a  solution  of  zinc  chloride  ? 

10.  Mention  two  ways  by  which  zinc  sulphide  can  be  formed. 

11.  Why  will  not  hydrogen  sulphide  completely  precipitate 
zinc,  as  zinc  sulphide,  from  a  solution  of  zinc  sulphate  ? 

12.  Explain  the  fact  that  water  solutions  of  zinc  sulphate 
give  an  acid  reaction. 

13.  Describe  a  test  for  zinc. 

14.  How  many  grams  of  zinc  would  be  required  to  replace 
the  hydrogen  contained  in  15  grams  of  sulphuric  acid  ?     How 
many  liters  of  hydrogen  would  be  formed  ? 

MERCURY 

SUMMARY 

Atomic  weight  200.  Valence  1  or  2.  Melting  point  -  39°. 
Boiling  point  357°.  Specific  gravity  13.6. 

Mercury  occurs  as  the  sulphide,  from  which  it  is  extracted  by 
roasting. 

It  is  the  only  metal  that  is  a  liquid  at  ordinary  temperatures. 

Mercury  combines  readily  with  sulphur  and  the  halogens.  It 
combines  with  oxygen  at  temperatures  a  little  below  its  boiling 
point.  Concentrated  nitric  acid  is  the  only  acid  that  has  much 
effect  on  mercury  at  ordinary  temperatures. 


EXERCISES  357 

Mercury  is  used  in  scientific  and  electrical  instruments  ;  in  the 
preparation  of  pigments  and  amalgams,  and  for  the  extraction  of 
gold. 

Calomel)  mercurous  chloride,  is  used  in  medicine. 

Corrosive  sublimate,  bichloride  of  mercury,  or  mercuric  chloride, 
is  a  deadly  poison  and  is  used  as  a  germicide. 

EXERCISES 

1.  Write  the  equation  for  the  extraction  of  mercury  from 
cinnabar. 

2.  What  properties  of  mercury  make  it  suitable  for  use  in 
thermometers  ?     In  barometers  ? 

3.  What  is  an  amalgam  ? 

4.  Under  what  circumstances  is  it  desirable  to  collect  a  gas 
by  the  displacement  of  mercury  ?     Why  is  it  more  difficult  to 
collect  a  gas  by  the  displacement  of  mercury  than  by  the  dis- 
placement of  water  ? 

5.  What  would  be  a- simple  way  of  testing  a  solution  for 
the  presence  of  a  mercury  salt  ? 

6.  Why  is  mercuric  oxide  used  in  paints  for  ship  bottoms  ? 

7.  Calculate  the  percentage  composition  of  the  two  chlorides 
of  mercury.     What  law  is  illustrated  by  the  composition  of 
these  compounds  ? 

8.  Why  do  surgeons  often  wash  their  hands  in  a  solution 
of  mercuric  chloride  before  performing  an  operation  ? 

9.  Why  should  bichloride  of  mercury  tablets  never  be  kept 
in  a  medicine  closet  ? 


CHAPTER   XXX 

IRON  AND  STEEL 

387.  Occurrence  of  Iron.  —  A  consideration  of  the  enor- 
mous quantity  of  iron  used  annually 'for  an  almost   un- 
limited number  of  purposes,  will  show  how  impossible  our 
present  civilization  would  be  without  this  metal. 

Native  iron  occurs  in  igneous  rocks  in  pieces  varying 
in  size  from  small  grains  to  that  of  a  mass  found  in  Green- 
land which  weighed  more  than  a  ton.  As  iron  rapidly 
corrodes  when  exposed  to  moist  air,  native  iron  is  not  of 
common  occurrence,  but  compounds  of  iron  are  common. 
The  red  and  yellow  colors  of  soils  are  generally  due  to 
oxides  and  silicates  of  iron.  Nearly  all  meteorites  con- 
tain iron  alloyed  with  nickel.  The  principal  ore  of  iron 
is  hematite  mixed  with  other  minerals,  such  as  silica  and 
clay. 

388.  Formation  of  Iron  Deposits.  —  When  water  perco- 
lates through  a  soil  containing  much  vegetable  matter,  it 
takes  up  substances  capable  of  reducing  ferric  compounds 
to  ferrous  compounds.     When   water  containing  carbon 
dioxide  comes  in  contact  with    the  ferrous  compounds, 
ferrous  acid  carbonate,  FeH2(CO3)2,  is  formed,  which  is 
soluble.     In  this  way  iron  is  dissolved  out  of  the  soil. 
If  water  containing  acid  ferrous  carbonate  collects  in  a 
warm  place  not  in   contact   with  air,    carbon    dioxide   is 
driven   off   and   ferrous    carbonate    (siderite),    which   is 
insoluble  in  water,  may  be  deposited.     When  water  con- 

358 


SMELTING   OF  IRON  ORE  359 

taining  ferrous  acid  carbonate  is  exposed  to  the  air,  ferric 
hydroxide  is  formed : 

4  FeH2(C03)2  +  2  H2O  +  O2  — *-  4  Fe(OH)3  +  8  CO2 

This  may  be  deposited,  and,  on  becoming  dry,  may  lose 
sufficient  oxygen  and  hydrogen  in  the  form  of  water  to 
convert  it  into  hydrated  ferric  oxide  (limonite),  2  Fe2O3 
3  ELjO,  or  into  ferric  oxide  (hematite),  Fe2O3 : 

4  Fe(OH)3  — >-  2  Fe2O3  .  3  H2O  +  3  H2O 
2  Fe(OH)3  — »-  Fe203  +  3  H2O 

389.  Smelting  is  a  general  term  used  to  designate  one  or 
more  operations  carried  on  in  a  furnace  for  the  purpose  of 
obtaining  an  element  (nearly  always  a  metal)  from  an  ore. 

390.  Smelting  of  Iron  Ore.  —  When  impure  hematite,  for 
example,  is  to  be  smelted,  it  is  necessary  to  accomplish 
two  main  operations.     These  are  :   (a)  to  reduce  the  oxide, 
for  which  purpose  carbon  in  the  form  of  coke  is  used ;  and 
(6)  to  separate  the  other  minerals  that  occur  in  the  ore ; 
for  this  purpose  a  substance  called  a  flux  is  employed. 
The  flux  also  aids  in  the  fusion  of  the  ore. 

When  the  ore  contains  sand  (silica,  SiO2),  limestone  is 
used  as  a  flux.  On  being  heated  in  the  furnace,  the  lime- 
stone is  decomposed  into  carbon  dioxide  and  calcium 
oxide : 

CaCO3  — >-  CO2  +  CaO 

The  basic  oxide,  CaO,  combines  with  the  acidic  oxide, 
SiO2,  and  forms  calcium  silicate. 

If  the  ore  contains  basic  material,  silicon  dioxide  may 
be  used  as  a  flux,  and  the  removal  of  the  impurity  be 
effected  in  a  way  analogous  to  that  just  described. 


360 


IE  ON  AND   STEEL 


391.  Manufacture  of  Cast  Iron.  —  Iron  ores  are  smelted  in 
a  blast  furnace  (Fig.  116)  which  has  a  steel  shell  from  75 
to  90  feet  high,  lined  with  a  thick  layer  of  fire  brick. 

Cold  water  is  made  to  cir- 
culate through  hollow  cast- 
ings built  into  the  fire  brick 
in  the  part  of  the  furnace 
where  the  most  energetic 
chemical  action  takes  place 
during  the  smelting.  This 
is  just  above  the  point  where 
pipes  called  tuydres  admit 
powerful  blasts  of  hot,  dry 
air  into  the  furnace.  The 
name  "blast  furnace"  is  due 
to  these  blasts  of  air. 

A  blast  furnace,  once 
started,  is  kept  in  contin- 
uous operation  day  and 
night,  seven  days  in  the 
week,  until  it  is  necessary  to 
shut  down  in  order  to  make 
repairs.  The  charge  of  ore, 
coke,  and  flux  is  dropped  in 
at  the  top  of  the  furnace 
from  time  to  time.  The 
heated  blast  of  air  which 
enters  the  furnace  through 
the  tuyeres  comes  in  contact 

with  the  burning  coke  and 
FIG.  116.  —  BLAST  FURNACE.  f  •,          T      •  i         i_  •  i, 

forms  carbon  dioxide,  which 

is  immediately  reduced  to  carbon  monoxide  by  the  excess 
of  hot  carbon.  The  carbon  monoxide  and  remaining 
carbon  reduce  the  iron  oxide  to  iron  : 


THE  BLAST  FURNACE 


361 


Fe2O3  +  3  C  - 

Fe203  +  3  CO 


2  Fe  +  3  CO 
*-  2  Fe  +  3  CO2 


Simultaneously  with  the  reduction  of  the  ferric  oxide, 
some  silica  is  reduced  to  silicon,  and  combines  with  the 
iron.  The  iron  also 
takes  sulphur  and  phos- 
phorus from  the  ore 
and  coke;  and  from  2  to 
7  %  of  carbon  enters  it 
from  the  coke.  This 
impure  iron  settles  to 
the  bottom  of  the  fur- 
nace, from  which  place 
it  is  drawn  off  from 
time  to  time  through  a 
hole,  called  a  tap  hole. 
The  stream  of  white- 
hot,  molten  metal  is  cast 
into  ingots  called  pigs 
(Fig.  117).  The  product  is  known  as  pig  iron  or  cast  iron. 
The  limestone  flux  mentioned  above  combines  with  the 
silica  and  other  acidic  substances  in  the  ore,  and  produces 
the  slag.  Both  slag  and  the  molten  cast  iron  collect  in  the 
crucible  of  the  furnace,  the  slag  floating  on  the  heavier  iron. 

392.  The  Blast  Furnace.  —  The  desirability  of  cheap  and 
rapid  production  of  cast  iron  has  brought  the  blast  fur- 
nace to  its  present  perfection.  The  opening  at  the  top 
through  which  the  charging  is  done  is  closed  by  a  cup  and 
cone  arrangement  (Fig.  116).  The  best  modern  furnaces 
have  an  air  lock  at  the  top,  closed  above  and  below  by  a 
cup  and  cone.  In  such  a  furnace,  the  charge  can  be  let 
into  the  air  lock,  and  then,  after  the  opening  at  the  top  is 


Copyright  by  the  Keystone  'View  Co. 

FIG.  117.  —  PIG  IRON  IN  A   METAL  YARD. 


362 


IRON  AND   STEEL 


closed,  can  be  allowed  to  drop  into  the  furnace.  This 
method  prevents  the  escape  of  gas  during  charging.  The 
gases  produced  during  the  smelting,  which  contain  about 
20  %  carbon  monoxide,  are  conveyed  away  from  near  the 


FIG.    118.  —  CASTING    MACHINE,    SHOWING    METAL    RUNNING    FROM    LADLE 
INTO  MOLDS  CARRIED  ON  AN  ENDLESS  CHAIN. 

top  of  the  furnace  through  a  large  flue.  This  furnace 
gas  is  burned  to  supply  heat  for  the  air  blast,  and  under 
the  boilers  to  generate  steam  for  the  engines  which  com- 
press the  air  for  the  tuyeres. 

The  crucible  in  which  the  molten  iron  and  slag  collect 
is  about  16  feet  in  diameter.  Holes  are  drilled  through 
its  sides  for  the  removal  of  slag  and  iron.  The  process  is 


COMPOSITION  AND  PROPERTIES  OF  CAST  IRON   363 

called  tapping  the  furnace.  As  soon  as  the  iron  or  slag 
has  been  removed,  the  tap  hole  is  closed  by  a  clay  plug 
which  is  instantly  hardened  by  the  heat.  The  slag  is 
tapped  off  about  every  two  hours,  and  the  iron  every  four 
to  six  hours.  From  80  to  300  tons  of  metal  are  drawn 
off  per  day.  If  the  iron  is  to  be  used  in  making  steel 
in  works  near  by,  it  is  often  carried  directly  there  in  large 
ladles  ;  otherwise  it  is  run  into  pigs,  which  may  be  cast  in 
sand,  or,  by  means  of  a  casting  machine,  in  iron  molds 
(Fig.  118). 

393.    Composition  and  Properties  of   Cast  Iron.  —  If  the 

iron,  after  being  drawn  from  the  blast  furnace,  is  suddenly 
cooled,  a  white  cast  iron  is  obtained.  The  carbon  in  white 
cast  iron  is  in  chemical  combination  with  the  iron  as  iron 
carbide,  Fe8C.  When  the  molten  iron  is  cooled  slowly,  most 
of  the  carbon  separates  in  the  form  of  graphite,  and  the 
product  is  known  as  gray  cast  iron.  As  iron  carbide  is  a 
very  hard  compound,  white  cast  iron  is  harder  than  gray. 
Cast  iron  contains  considerable  carbon,  always  over 
2%  and  seldom  above  5%.  It  is  the  form  of  iron  most 
easily  melted,  and  expands  when  it  passes  from  a  liquid 
to  a  solid  state.  Therefore,  when  molten  cast  iron  is 
poured  into  a  mold,  and  allowed  to  solidify,  the  metal 
readily  takes  the  shape  of  the  mold.  In  making  castings 
allowance  has  to  be  made  for  shrinkage,  because  iron 
contracts  on  further  cooling  after  it  solidifies.  Cast  iron 
is  not  malleable  and  can  be  neither  welded  nor  tempered. 
It  is  used  for  casting  articles,  such  as  stoves  and  orna- 
mental iron  work,  which  are  not  to  be  subjected  to  shock. 
Wrought  iron  and  steel  are  made  from  cast  iron.  Iron 
sulphide  is  generally  formed  during  the  smelting  of  an 
iron  ore  and  alloys  with  the  iron.  Sulphur  makes  iron 
"red  short"  or,  in  other  words,  brittle  when  red  hot. 


364 


IRON  AND   STEEL 


If  the  ore  contains  phosphorus,  phosphide  of  iron  is  formed 
and  dissolves  in  the  iron  produced  in  the  blast  furnace. 
Phosphorus  makes  iron  "  cold  short,"  that  is,  brittle  when 
cold.  Since  both  phosphorus  and  sulphur  are  harmful 
to  wrought  iron  and  steel,  they  must  be  removed  when 
these  high-grade  products  are  to  be  obtained. 


FIG.   119.  —  REVERBERATORY  FURNACE. 

394.  Manufacture  of  Wrought  Iron.  —  Wrought  iron  is 
made  in  a  reverberatory  furnace  (Fig.  119)  by  heating 
cast  iron  on  a  layer  of  iron  oxide.  The  flames  of  the 
burning  fuel  pass  over  the  furnace  charge  and  the  heat 
reverberates  between  it  and  the  roof  of  the  furnace.  The 
charge  is  thus  melted  without  coming  in  contact  with  the 
fuel.  Under  these  circumstances,  the  greater  part  of  the 
carbon  contained  in  the  cast  iron  is  oxidized  to  carbon 
monoxide  and  passes  off.  If  necessary,  a  basic  lining  and 
a  basic  slag  are  used  to  remove  sulphur,  phosphorus,  and 
silica  from  the  iron.  Basic  oxides  fuse  with  the  acidic 
oxides  to  form  salts  which  enter  the.  slag.  The  iron 
becomes  pasty,  because  pure  iron  has  a  higher  melting 
point  than  impure.  The  molten  mass  in  the  furnace  is 
stirred  or  puddled  and  the  pasty  iron  is  gathered  into 
large  balls  called  blooms.  These  are  removed  from  the 
furnace  and  nearly  freed  from  slag  by  a  process  of 
squeezing  and  working  under  a  trip  hammer.  The 
iron  is  then  rolled  so  as  to  give  the  product  a  fibrous 


BESSEMER   STEEL  365 

structure,  by  causing  the  remaining  slag  to  be  distributed 
through  the  iron  in  the  form  of  fine  threads.  This  small 
portion  of  slag  aids  in  the  process  of  welding  iron. 

395.  Properties  and  Uses  of  Wrought  Iron.  —  Wrought  iron 
is   the  purest  form  of  commercial  iron.     Good  varieties 
contain  not  more  than  0.3%  of  carbon. 

When  wrought  iron  is  heated,  it  becomes  plastic  before 
melting.  When  in  this  condition,  two  pieces  on  being 
hammered  together  adhere  firmly,  provided  some  substance, 
such  as  sand,  is  placed  on  the  iron  to  dissolve  the  thin 
coating  of  iron  oxide  that  forms  on  the  heated  sur- 
face. This  process  is  called  welding.  Plastic  wrought 
iron  can  be  hammered  into  various  shapes,  rolled  into  bars, 
and  drawn  into  wire.  Wrought  iron  is  tough  and  can  be 
bent  or  stretched  without  breaking.  It  can  very  easily  be 
converted  into  a  temporary  magnet.  Wrought  iron  is 
used  to  make  anchors,  chains,  wire,  and  other  articles  which 
are  intended  to  withstand  sudden  and  severe  strains.  As 
wrought  iron  can  be  readily  forged  and  welded,  it  is  the 
iron  used  by  the  blacksmith.  It  cannot  be  tempered. 

396.  Bessemer  Steel.  —  Much  cast  iron  is  converted  into 
Bessemer  steel,  or  more  properly  Bessemer  iron.     About 
fifteen  tons  of  molten  cast  iron  are  poured  into  a  Bessemer 
converter  (Fig.  120),  which  is  an  egg-shaped  furnace  built 
of  wrought  iron  plates  and  lined  with  a  thick  layer  of 
refractory  material.     The  bottom  is  perforated  with  holes 
so  that  streams  of  air  can  be  blown  through  the  molten 
metal.     The  blast  lasts  from  eight  to  ten  minutes,  during 
which  time  the  oxygen  of  the  air  unites  with  the  silicon, 
carbon,  and  other  impurities  in  the  cast  iron,  leaving  nearly 
pure  iron.     The  heat  of  combustion  raises  the  temperature 
of  the  metal  to  a  high  degree,  producing  what  is  known  as 
the  "boil."     Just  as  the  iron  commences  to  burn  the  blow 


366 


IRON  AND  STEEL 


is  stopped,  and  the  desired  amount  of  a  cast  iron  called 
spiegeleisen,  which  is  rich  in  carbon  and  manganese,  is 
added.  The  blast  of  air  is  forced  through  the  mass  for 
a  short  time  to  thoroughly  mix  the  ingredients.  The 
spiegeleisen  furnishes  the  desired  amount  of  carbon,  and 
the  manganese  unites  with  any  dissolved  oxygen  present. 

The  oxygen  is  thus  pre- 
vented from  escaping  and 
producing  blowholes 
when  the  mass  cools.  The 
manganese  also  improves 
the  quality  of  the  metal. 
At  the  end  of  the  process, 
the  converter  is  turned 
and  the  contents  poured 
into  a  ladle  and  cast. 

If  the  pig  iron  contains 
sufficient  sulphur  and 
phosphorus  to  materially 
injure  the  quality  of  the  Bessemer  iron,  the  converter  is 
lined  with  basic  material.  The  use  of  a  basic  lining  was 
discovered  by  Thomas  and  Gilchrist,  and  the  process  is 
named  for  them.  The  slag  produced,  known  as  Thomas 
slag,  contains  basic  phosphates  and  is  of  value  as  a  fertilizer. 

397.  Steel  by  Open  Hearth  Process.  —  Much  steel  is  now 
made  by  the  open  hearth  process.  An  open  hearth  fur- 
nace (Fig.  121)  has  a  large  bed  lined  with  fire  brick  and 
sand  on  which  the  charge  is  placed.  By  the  aid  of  a  regen- 
erative heating  system,  a  higher  temperature  is  obtained 
than  would  otherwise  result.  This  device  is  used  in  many 
modern  furnaces.  Gas  is  used  as  fuel  and  is  heated  before 
entering  the  furnace  by  passing  through  a  checkerwork  of 
hot  fire  brick.  The  heated  gas  is  passed  into  the  furnace 


FIG.  120.  —  BESSEMER  CONVERTER. 


STEEL  BY  OPEN  HEARTH  PROCESS 


367 


through  a  pipe,  while  air  that  has  been  similarly  heated 
enters  through  another  flue.  The  burning  gas  passes 
over  the  charge  on  the  furnace  bed  and  the  hot,  gaseous 
product  escapes  through  checkerworks  which  are  a  dupli- 
cate of  those  used  to  heat  the  gas  and  air.  One  set  of 
checkerwork  is  thus  raised  to  a  high  temperature  by  the  hot 


FIG.  121.  —  OPEN  HEARTH  FURNACE  WITH  REGENERATORS. 

combustion  products,  while  the  other  is  being  cooled  as  it 
heats  the  gas  and  air  about  to  enter  the  furnace.  About 
every  twenty  minutes  the  direction  of  the  gas  and  air  is 
reversed  by  means  of  a  system  of  valves,  so  that  gas  and 
air  pass  through  the  recently  heated  checkerwork  while  the 
flame  from  the  furnace  passes  through  the  one  just  cooled. 
The  furnace  charge  consists  of  scrap  steel,  pig  iron,  and 
iron  ore.  The  scrap  steel  is  placed  on  the  bottom  in  order 
to  protect  it  from  the  oxidizing  action  of  the  flame.  The 
manganese  and  silicon  are  oxidized  by  the  flame,  while 


368  IRON  AND  STEEL 

the  iron  ore  is  active  in  furnishing  oxygen  to  consume 
the  carbon.  The  process  consumes  from  eight  to  twelve 
hours  and  is  watched  and  controlled  most  carefully  by  the 
operator.  Samples  of  metal  are  repeatedly  taken  from  the 
furnace  and  examined  to  determine  when  the  impurities 
have  been  removed  and  the  carbon  has  been  reduced 
to  the  desired  amount.  In  case  the  pig  iron  contains 
phosphorus,  a  basic  furnace  lining  can  be  used  as  in  the 
Bessemer  process.  The  steel  produced  is  of  much  better 
quality  than  the  metal  made  by  the  Bessemer  process  and 
is  suitable  for  the  manufacture  of  connecting  rods,  shafts, 
armor  plate,  heavy  ordnance,  etc.,  where  great  strength 
and  ability  to  stand  vibration  are  required.  It  can  be 
forged  and  tempered.  The  percentage  of  carbon  varies 
from  0.05  in  soft  steel  to  2.0  in  hard. 

398.  Crucible  steel  is  made  in  graphite  crucibles.  The 
materials  used  are  high-grade  wrought  iron,  scrap  steel, 
and  carbon,  in  the  form  of  hard  wood  charcoal,  coke,  or 
graphite.  When  pure  iron  is  heated  to  a  temperature 
above  850°,  it  is  converted  into  an  allotropic  form  of  iron 
that  is  capable  of  absorbing  carbon.  The  carbon  at 
first  forms  a  solid  solution  with  the  iron,  but  after  the 
carbon  has  reached  0.8  %  of  the  mass,  it  separates  as  iron 
carbide,  Fe3C.  Steel  always  contains  iron  carbide,  which 
may  be  either  dissolved  in  the  iron,  or  gathered  in  par- 
ticles throughout  the  mass.  In  general,  the  more  iron 
carbide  the  steel  contains  the  harder  it  is.  In  the  manu- 
facture of  crucible  steel  (Fig.  122)  the  iron  is  melted,  a 
temperature  of  1500°  C.  being  maintained  for  from  two  to 
six  hours.  The  heating  is  continued  until  sufficient  car- 
bon has  been  absorbed,  from  the  charcoal  and  the  crucible, 
to  make  the  desired  quality  of  steel.  Special  crucible  steels 
are  made  by  the  addition  of  various  substances  to  the 


SPECIAL   STEELS 


369 


crucible  charge.  Crucible  steels  are  of  high  grade  and 
are  used  in  making  fine  edged  tools,  springs,  automobile 
parts,  bridge  cables,  etc. 

399.  Special  Steels.  —  Certain  of  the  less  familiar  metals 
when  added  in  small  quantities  produce  steels  of  great 
hardness,  toughness,  or  tensile  strength.  More  than  8  % 
of  manganese  in  a  steel,  or  chromium  in  smaller  amount, 


Courtesy  of  the  Crucible  Steel  Co.  of  America. 

FIG.  122.  —  CRUCIBLE  MELTING  FURNACES. 

gives  great  hardness  to  the  steel.  Tungsten  and  molyb- 
denum are  used  in  making  self-hardening  steels.  Tools 
made  from  self -hardening  steels  retain  a  fine  cutting  edge 
without  being  tempered. 

Manganese,  chromium,  vanadium,  and  nickel  steels  are 
used  for  safes,  armor  plates,  and  parts  of  machinery 
subject  to  great  stress  or  vibration,  as  shafts  or  auto- 
mobile bearings.  Deposits  of  iron  ore  that  had  been 
regarded  as  too  refractory  to  work  have  been  made  valu- 
able by  the  demand  for  these  special  steels. 


370 


IRON  AND   STEEL 


400.  Electric  Refining  of  Steel.  —  Various  types  of  furnaces 
are  at  present  used  for  the  refining  of  steel.  Each  type 
has  some  advantage  over  the  other  types.  Electric 
furnaces  seem  especially  adapted  to  the  production  of 

high-grade  steels  from 
low-grade  materials  con- 
taining sulphur  and 
phosphorus. 

Heroult  was  first  to 
construct  a  successful 
arc  and  resistance  fur- 
nace for  the  refining  of 
steel.  The  Heroult 
furnace  has  a  capacity 
up  to  15  tons  of  steel  at 
FIG.  123. —  GIROD  ELECTRIC  FURNACE.  a  charge.  Carbon  elec- 
trodes are  used.  These  cannot  come  in  contact  with 
the  iron,  since,  at  the  temperature  of  the  furnace,  the 
carbon  would  rapidly  enter  into  combination  with  the 
iron.  -In  the  Heroult  furnace  a  basic  lining  is  used  and 
a  basic  slag  covers  the  steel  to  be  refined.  The  lower 
ends  of  the  electrodes  dip  into  the  slag  on  top  of  the  steel 
to  such  a  depth  that  the  current  arcs  through  the  slag  to 
the  iron  underneath  one  electrode,  passes  through  the  iron 
to  a  point  beneath  another  electrode,  and  then  arcs  from 
the  iron  through  the  slag  to  it.  The  heat  generated  melts 
the  furnace  charge,  and  sulphur,  phosphorus,  and  other 
acidic  impurities  are  readily  removed  by  the  basic  slag. 

The  Girod  furnace  (Fig.  123)  has  upper  electrodes 
made  of  carbon.  These  dip  into  the  slag  on  top  of  the 
steel  to  be  refined,  as  in  the  case  of  the  Heroult  furnace. 
In  the  Heroult  furnace,  the  carbon  electrodes  are  widely 
separated  and  of  different  polarity,  while  in  the  Girod 
furnace  the  carbon  rods  are  near  together,  and  are  of  the 


TEMPERING   OF  STEEL  371 

same  polarity.  The  Girod  furnace  has  also  electrodes  of 
soft  iron  placed  at  the  bottom  of  the  furnace  near  the  outer 
edge.  The  carbon  electrodes  are  connected  in  parallel,  so 
that  they  are  always  of  the  same  polarity.  The  iron 
electrodes,  which  are  also  connected  in  parallel,  have 
the  opposite  polarity.  The  portion  of  the  iron  elec- 
trodes that  extends  outside  the  furnace  is  water-cooled. 
The  current  arcs  from  the  carbon  electrodes  through 
the  slag  to  the  steel  beneath  and  then  passes  to  the  iron 
electrodes.  The  charge  and  chemical  action  is  similar 
to  that  in  the  Heroult  furnace.  In  both  furnaces  the 
only  effect  of  the  electric  current  is  to  develop  heat. 

401.  Tempering  of  Steel.  —  The  process  of  varying  the 
hardness  of  steel  by  heat  treatment  is  termed  tempering. 
As  has  already  been  mentioned,  all  steel  contains  iron 
carbide,  Fe3C,  a  very  hard  substance  that  readily  dis- 
solves in  pure  iron  at  a  high  temperature  (above  670°  C.). 
When  all  of  the  iron  carbide  contained  in  the  steel  is  in 
solution  and  the  product  is  suddenly  cooled,  further  change 
is  prevented,  and  a  steel  is  obtained  that  is  as  hard  as  it  is 
possible  to  obtain  by  heat  treatment  alone.  If  a  solid  solu- 
tion of  iron  carbide  in  pure  iron  is  cooled  slowly,  a  change 
takes  place  below  670°  C.,  and  the  iron  carbide  gradually 
passes  out  of  solution  and  collects  in  small  particles  in  the 
iron.  We  now  have  amass  of  soft  iron  containing  crystals  of 
iron  carbide,  and  the  pure  iron  imparts  the  property  of  soft- 
ness to  the  mass.  The  conglomerate  of  iron  and  iron  carbide 
is  far  softer  than  the  solid  solution  of  iron  carbide  in  iron. 
If  a  hard  steel  is  heated  to  a  temperature  between  430°  C. 
and  670°  C.,  the  iron  carbide  slowly  separates  from  the  solid 
solution  and  the  mass  is  softened,  that  is,  tempered  by  heat. 
The  amount  of  iron  carbide  that  separates  depends  upon  the 
temperature  and  the  length  of  time  used  in  the  heating. 


372 


IRON  AND   STEEL 


Heating  for  a  long  time  at  moderate  temperatures,  or 
quick  heating  to  the  higher  temperatures  below  670°  (the 
temperature  at  which  iron  carbids  dissolves  in  iron)  ac- 
complishes the  same  result,  viz.  the  decomposition  of  the 
iron  carbide.  The  process,  however,  can  be  stopped  at 
any  time  by  a  sudden  cooling,  and  a  steel  of  the  desired 
hardness  obtained.  The  temperature  can  be  estimated  by 
a  play  of  colors  ranging  from  yellow  to  brown,  red,  pur- 
ple, violet,  and-blue,  to  gray,  which  appear  when  the  metal 
is  heated.  These  colors  are  due  to  the  formation  of  thin 
layers  of  iron  oxide,  causing  interference  colors.  The 
colors  follow  each  other  when  the  metal  is  cooled,  and  as 
soon  as  the  right  color  is  obtained  the  process  is  stopped 
by  dipping  the  article  into  either  water  or  oil. 


COLOR 

TEMPERATURE 

STEEL  USED  FOR 

Pale  yellow 
Full  yellow 
Brown 

430°-450° 
470° 
490°-510° 

Razors 
Penknives 
Shears  and  tools  for  brasswork 

Purple 
Blue 
Blue-black 

520° 
530°-570° 
610° 

Table  knives 
Watch  springs  and  sword  blades 
Saws  an  d  other  wood-working  tools 

The  yellow  tints  give  very  hard  but  brittle  steels,  while, 
as  we  proceed  toward  the  blue,  the  steel  is  softer  but 
tougher.  The  films  are  usually  removed  by  grinding,  but 
are  seen  on  some  saws  and  springs. 

402.  Classification  of  Iron  and  Steel.  —  Commercial  iron  is 
commonly  classified  as  cast  iron,  wrought  iron,  and  steel. 
Cast  iron  contains  the  highest  percentage  of  carbon, 
wrought  iron  the  least,  and  steel  usually  stands  between. 
Chemical  composition,  however,  is  not  a  sure  way  of  dis- 


COMPARATIVE    TABLE   OF  PROPERTIES        373 


tinguishing  these  forms,  as  some  steels  contain  less  carbon 
than  certain  wrought  irons.  Moreover,  the  condition  the 
carbon  is  in,  whether  free  or  combined  with  the  iron,  and 
whether  iron  carbide  is  segregated  or  is  in  solution,  is  as 
important  a  factor  as  its  percentage.  Knowledge  gained 
from  a  careful  study  of  the  structure  of  a  polished  and 
etched  section  under  a  microscope  is  used  as  a  guide  to 
the  true  nature  of  an  iron  or  steel.  This,  and  some  recent 
principles  developed  by  physical  chemistry,  have  put  the 
iron  industry  on  a  scientific  basis.  At  best,  the  classifica- 
tion of  iron  is  difficult,  and  unless  we  classify  a  product 
according  to  the  process  by  which  it  is  made,  we  shall  be 
confused  by  the  many  varieties  of  steel  and  iron  that 
grade- into  one  another. 

COMPARATIVE   TABLE  OF  PROPERTIES 


CAST  IRON 

WROUGHT  IRON 

STEEL 

Low-carbon 

High-carbon 

Carbon,  per 

2%  to  7.5% 

0.05%  to  0.3% 

0.05%  to  0.8% 

0.8%  to  2.0% 

cent. 

Melting 

1200°  C. 

1500°  C. 

1500°  C. 

1400°  C. 

point,  ap- 

proximate 

Structure 

Crystalline 

Fibrous 

Granular  or 

Granular 

fibrous 

Hardness 

Very  hard 

Soft 

Moderately 

Hard,  if  tem- 

soft- 

pered 

Possible 

Can  be  cast, 

Can  be 

Can  be  cast 

Can  be  cast 

treatment 

but  not 

welded,  but 

and 

and  tem- 

when 

welded  or 

not  cast  or 

welded, 

pered.  Not 

heated 

tempered 

tempered 

but  not 

easily 

tempered 

welded 

Uses 

Castings, 

Wire,  electro- 

Structural 

Tools, 

bases  and 

magnets 

steel,  wire, 

springs, 

columns 

and  maDe- 

nails,  sheet 

permanent 

able  iron 

magnets 

374  IRON  AND  STEEL 

SUMMARY 

Welding  is  the  process  of  joining  two  pieces  by  heating  the  sur- 
faces to  be  joined  until  they  soften,  and  then  causing  them  to  unite 
by  pressure  or  by  hammering. 

Tempering  is  the  varying  of  the  hardness  of  a  substance,  nearly 
always  steel,  by  heat  treatment.  The  hardness  of  steel  depends 
upon  the  amount  of  iron  carbide  the  steel  contains,  and  upon 
whether  the  iron  carbide  is  segregated  or  in  solution. 

EXERCISES 

1.  Why  does  not  iron  occur  to  any  extent  in  a  free  state  ? 

2.  Why  was  wrought  iron  probably  the  first  form  of  iron 
worked  by  man  ? 

3.  What  becomes  of  the  ashes  that  would  ordinarily  result 
from  the  combustion  of  coke  when  the  coke  is  burned  -in  the 
blast  furnace  ? 

4.  Why  is  it  necessary  to  produce  slag  in  working  a  blast 
furnace  ? 

5.  What  would  be  the  constituents  of  a  furnace  charge  for 
smelting  an  ore  consisting  of  ferrous  carbonate  mixed  with 
calcium  carbonate  ?     Explain. 

6.  Why  cannot  wrought  iron  be  tempered  ? 

7.  What  is  the  shape  of  the  slag  left  when  wrought  iron 
corrodes  ?     Is  the  slag  left  in  the  same  shape  when  cast  iron 
rusts  away  ? 

8.  Why  does  the  temperature  of  the  Bessemer  converter 
rise  when  cold  air  is  blown  through  the  cast  iron  in  it  ? 

9.  For  what  purposes  is  Bessemer  steel  inferior  to  crucible 
steel?     Why? 

10.  What  kind  of  iron  would  you  use  for  the  manufacture 
of  dynamo  cores?     Steam  radiators?     Bridge  cables?     An- 
chors ?     Springs  ?     Chisels  ?     Hammered  iron  work  ? 

11.  Why  are  the  carbon  electrodes  of  an  electric  furnace 
used  for  the  refining  of  steel  not  permitted  to  dip  into  the 
molten  iron  ? 


CHAPTER  XXXI 

IRON  AND  ITS  COMPOUNDS 

403.  Pure  Iron.  —  Pure   iron  may  be  prepared   by   the 
reduction   of  pure  iron  compounds,  as  the  oxalate,  in  a 
stream  of  hydrogen ;  or  electrolytic  iron  may  be  deposited 
from  solutions  of  certain  iron  salts. 

Pure  iron  is  a  white,  lustrous  metal  which  is  very  tough 
and  which  fuses  only  at  a  high  temperature.  It  is  malle- 
able, ductile,  and  may  be  temporarily  magnetized. 

In  dry  air,  pure  iron  does  not  rust,  but  in  moist  air 
rusting  proceeds  rapidly,  particularly  if  carbon  dioxide 
is  present.  Iron  decomposes  water  very  slowly  at  ordi- 
nary temperatures,  but  at  higher  temperatures  the  reac- 
tion proceeds  rapidly.  With  cold,  dilute  acids,  such  as 
hydrochloric  and  sulphuric,  hydrogen  is  evolved  and  a  fer- 
rous salt  is  formed.  With  hot,  or  more  concentrated  acids, 
certain  reduction  products  may  be  produced.  When  cast 
iron  is  dissolved  in  acids,  the  unpleasant  odor  is  due  to  the 
formation  of  hydrocarbons  and  to  sulphur  and  phosphorus 
compounds  from  impurities  in  the  iron. 

404.  Iron  Ions.  —  Iron  forms  two  kinds  of  ions,  —  biva- 
lent, Fe++,  and  trivalent,  Fe+++.       Bivalent   ions   result 
from  the  dissociation  of  ferrous  compounds,  and  trivalent 
ions   from   the  dissociation  of  ferric  compounds.     Com- 
pounds in  which  iron  has  a  valence  of  two  are  known  as 
ferrous  compounds;  those  in  which  the  valence  of  iron  is 
three  are  termed  ferric  compounds. 

375 


376  IRON  AND  ITS   COMPOUNDS 

405.  Oxides  of  Iron.  —  Ferrous  oxide,  FeO,  can  be  pre- 
pared by  the  reduction  of  ferric  oxide  with  hydrogen  or 
carbon  monoxide.     It  is  a  black  powder  which  cannot  be 
kept  in  air  on  account  of  the  ease  with  which  it  passes 
into  ferric  oxide. 

Ferric  oxide,  Fe2O3,  forms  the  most  important  ore  of 
iron.  It  can  be  readily  prepared  by  heating  ferric  hy- 
droxide, ferrous  carbonate,  or  ferrous  sulphide.  Ferric 
oxide  constitutes  the  coloring  matter  of  such  pigments  as 
Venetian  red,  Indian  red,  and  light  red.  When  ferrous 
sulphate  is  calcined,  a  form  of  ferric  oxide  known  as  rouge 
is  obtained.  Rouge  is  used  for  polishing  and  as  a  pigment. 
Limonite,  or  hydrated  ferric  oxide  (2  Fe2O3  •  3  H2O),  is 
found  in  nature  mixed  with  fine  clay  and  sand.  Such 
mixtures  constitute  the  pigment  yellow  ocher.  When  cal- 
cined, various  shades  of  yellow,  orange,  and  brown  are 
obtained.  These  are  sold  as  raw  sienna,  burnt  sienna, 
raw  umber,  and  burnt  umber. 

The  magnetic  oxide  of  iron,  Fe3O4,  occurs  in  nature  as 
lodestone.  It  is  formed  when  ferric  oxide  is  heated  to 
a  high  temperature  and  when  iron  is  burned  in  oxygen 
or  in  air.  It  constitutes  what  is  known  as  blacksmith's 
scale,  formed  when  red-hot  iron  is  worked.  When  steam 
is  passed  over  red-hot  iron,  hydrogen  is  liberated,  and  a 
firmly  adhering  film  of  magnetic  oxide  is  deposited  on 
the  iron.  This  film  prevents  the  rusting  of  the  iron 
under  it.  Russia  iron,  used  as  a  covering  for  locomotive 
boilers,  etc.,  is  iron  that  has  been  artificially  coated  with 
magnetic  oxide  of  iron. 

406.  Hydroxides  of  Iron.  —  Ferric  hydroxide  can  be  formed 
by  the  addition  of  a  base  to  a  solution  of  a  ferric  salt; 

FeCl3  +  3  NH4OH  — v  Fe(OH)3  +  3  NH4C1 


IRON  RUST  377 

It  is  precipitated  as  a  reddish  brown,  flocculent  compound, 
which,  on  drying,  changes  to  iron  rust.  Iron  rust  may  be 
considered  as  a  double  compound  of  ferric  oxide  and  ferric 
hydroxide.  It  is  probably  produced  in  a  manner  analogous 
to  that  described  for  the  natural  formation  of  hematite. 
Iron  dissolves  either  in  water  or  in  moisture  from  the  air, 
that  contains  carbonic  acid,  forming  acid  ferrous  carbonate: 

Fe  +  2  H2CO3  — ->-  FeH2(C03)2  +  H2 

This  substance,  on  drying  and  further  oxidation,  is  con- 
verted into  iron  rust.  If  we  represent  iron  rust  by  the 
formula  Fe2O3  •  2  Fe(OH)3,  the  chemical  equation  would  be 

4  FeH2(CO3)2  +  Oa— »-  Fea08  •  2  Fe(OH)3  +  H2O  +  8  CO2 

A  coating  of  rust  does  not  protect  the  iron  under  it. 
The  coating  does  not  adhere,  but  scales  off,  probably  be- 
cause carbon  dioxide,  the  real  cause  of  rusting,  is  contin- 
ually liberated  in  direct  contact  with  the  iron,  when  the 
action  has  once  started.  Thus  iron  rust  hastens  the  for- 
mation of  additional  rust. 

When  ferric  hydroxide  is  heated  to  a  red  heat,  it  is  con- 
verted into  ferric  oxide  and  water: 

2  Fe(OH)3  — >-  Fe2O3  +  3  H2O 

Ferrous  hydroxide,  Fe(OH)2,  appears  white  when  first 
precipitated,  but  soon  changes  to  dull  green  and  then  to 
brown,  by  oxidation. 

407.  Chlorides  of  Iron.  — Ferrous  chloride,  FeCl2,  is  formed 
when  iron  is  heated  in  hydrogen  chloride.  It  is  also  formed 
when  iron  is  dissolved  in  hydrochloric  acid  in  the  absence 
of  air.  It  can  be  crystallized  as  a  pale  green  compound, 
FeCl2  •  4  H2O,  unstable  in  air. 

Ferric  chloride,  FeCl3,  can  be  prepared  by  passing  chlo- 


378  IRON  AND  ITS   COMPOUNDS 

rine  over  hot  iron;  by  dissolving  iron  in  aqua  regia;  and 
by  dissolving  ferric  oxide  in  hydrochloric  acid.  When 
hydrogen  peroxide  is  added  to  a  solution  of  ferrous 
chloride  containing  hydrochloric  acid,  ferric  chloride  is 
instantly  formed.  Ferric  chloride  is  used  in  medicine, 
and  in  general  whenever  a  soluble  ferric  salt  is  required. 

408.  Change  of  Valence  by  Oxidation  and  Reduction.  —  The 

changes  in  valence  that  take  place  during  certain  re- 
actions give  an  extended  meaning  to  the  terms  oxida- 
tion and  reduction,  because  such  changes  in  valence  are 
often  brought  about  by  the  action  of  oxidizing  and  reduc- 
ing agents.  Hence  the  terms  oxidation  and  reduction  are 
often  used  to  express  change  in  valence.  In  this  sense,  an 
increase  in  the  valence  of  the  positive  part  of  the  molecule  is 
termed  oxidation;  a  decrease  in  the  valence  of  the  positive 
part  of  the  molecule,  reduction. 

The  terms  are  applied  to  reactions  in  which  oxygen 
takes  no  part.  If  ferric  chloride,  FeCl3,  is  treated 
with  nascent  hydrogen,  ferrous  chloride,  FeCl2,  and  hy- 
drochloric acid  are  produced : 

FeCl8  +  H  — ->-  FeCl2  +  HC1 

The  iron  atom  is  reduced  from  a  valence  of  three  in  the 
ferric  compound  to  a  valence  of  two  in  the  ferrous  com- 
pound. By  adding  nitric  acid  or  some  other  oxidizing 
agent  to  the  mixture  of  ferrous  chloride  and  hydrochloric 
acid,  the  ferrous  chloride  is  oxidized  to  ferric  chloride,  by 
the  addition  of  an  atom  of  chlorine,  thus  increasing  the 
valence  of  the  iron: 

2  FeCl2  +  2  HC1  +  O  — >-  2  FeCl3  +  H2O 

409.  Sulphates  of  Iron.  —Ferrous  sulphate,  FeSO4  .  7  H2O, 
is  a  by-product  in  many  industries.  Scrap  iron  is  added 


FERROCYANWES  379 

to  sulphuric  acid  that  has  been  used  in  the  refining  of 
petroleum,  or  for  cleaning  iron.  The  iron  is  dissolved, 
and  on  evaporating  the  solution,  crystals  of  green  vitriol, 
sometimes  called  copperas,  are  obtained.  Much  ferrous 
sulphate  is  used  in  the  manufacture  of  blue  pigments,  as  a 
mordant,  in  the  preparation  of  black  inks,  and  for  the 
precipitation  of  gold  from  solutions  of  its  chloride. 

When  solutions  of  ferrous  sulphate  and  tannic  acid  are 
mixed,  ferrous  tannate,  a  nearly  colorless  compound,  is 
formed.  On  exposure  to  the  air,  ferrous  tannate  is 
changed  to  ferric  tannate,  which  is  insoluble,  and  has  a 
black  color.  Ferrous  tannate  is  the  chief  ingredient  of 
iron  inks.  As  the  writing  would  not  at  first  be  visible  if 
a  solution  of  pure  ferrous  tannate  were  used,  some  dye  is 
added  to  give  the  ink  color.  On  exposure  to  the  air,  fer- 
ric tannate  is  formed,  which  gives  the  ink  its  permanent 
black  color. 

Ferric  sulphate,  Fe2(SO4)3,  is  formed  when  ferrous  sul- 
phate is  oxidized  in  the  presence  of  sulphuric  acid.  It  is 
used  with  ammonium  sulphate  in  the  preparation  of  ferric 
ammonium  alum,  NH4Fe(SO4)2  •  12  H2O. 

410.  Ferrocyanides.  —  On  igniting  a  mixture  of  nitroge- 
nous organic  matter,  scrap  iron  and  potassium  carbonate, 
cooling  the  mass,  and  then  treating  it  with  hot  water, 
potassium  ferrocyanide,  K4Fe(CN)6,  passes  into  the  solu- 
tion. When  the  solution  cools,  crystals  of  potassium 
ferrocyanide,  or  yellow  prussiate  of  potash,  separate. 
These  have  a  composition  represented  by  the  formula 
K4Fe(CN)6 . 3  H2O. 

A  solution  of  potassium  ferrocyanide  does  not  give  the 
usual  characteristic  reactions  of  iron  because  the  iron 
exists  as  a  part  of  a  complex  ion,  Fe  (CN)6-  .  When 
solutions  of  ferric  salts  and  potassium  ferrocyanide  are 


380  IRON  AND  ITS   COMPOUNDS 

brought  together,  a  deep  blue  precipitate,  ferric  ferro- 
cyanide,  or  Prussian  blue,  is  formed.  The  reaction  is 
made  use  of  in  testing  for  ferric  ions  (Fe+++): 

4  FeCl8  +  3  K4Fe(CN)6  —  ->-  Fe4[Fe(CN)6]3  +  12  KC1 

Prussian  blue  is  an  important  pigment.  Bluing,  used 
for  laundry  purposes,  sometimes  contains  Prussian  blue. 
When  the  clothes  with  which  it  is  used  are  not  thoroughly 
freed  from  soap,  the  alkali  of  the  soap  decomposes  the 
ferric  ferrocyanide,  precipitating  ferric  hydroxide  on  the 
cloth  and  producing  spots  of  iron  rust: 

Fe4[Fe(CN)6]3  -f  12  NaOH  —  •»- 

3  Na4Fe(CN)6  +  4  Fe(OH)3 

411.  Ferricyanides.  —  Potassium  ferricyanide,  or  red 
prussiate  of  potash,  K3Fe(CN)6,  can  be  prepared  by 
treating  a  solution  of  potassium  ferrocyanide  with 
chlorine: 

2  K4Fe(CN)6  +  C12  —  >-  2  KC1  +  2  K3Fe(CN)6 

Solutions  of  potassium  ferricyanide,  when  added  to  those 
of  ferrous  compounds,  give  a  blue  precipitate,  ferrous  ferri- 
cyanide, or  Turnbull's  blue  : 


3FeCl2  +  2K3Fe(CN)6—  ^6KC1  +  Fe8[Fe(CN)6]a 

412.  Blue  Prints,  or  ferrotypes,  the  simplest  substitutes 
for  the  silver  photographic  papers  (§  436),  owe  their  color 
to  the  formation  of  Turnbull's  blue. 

When  a  solution  containing  ferric  chloride  and  a  reduc- 
ing agent,  such  as  oxalic  acid,  is  exposed  to  the  sunlight, 
the  ferric  salt  is  reduced  to  a  ferrous  salt  : 

2  FeCl3  +  H2C2O4—  ^2  CO2  +  2  HC1  +  2  FeCl2 


BLUE  PRINTS  381 

When  a  sheet  of  paper  is  coated  in  a  darkened  room  with 
such  a  mixture,  dried  and  then  exposed  under  a  negative 
to  the  sunlight,  the  greatest  reduction  will  take  place 
where  the  light  is  brightest.  On  covering  the  exposed 
paper  with  a  solution  of  potassium  ferricyanide,  Turn- 
bull's  blue  will  develop  wherever  ferrous  iron  exists,  and 
the  depth  of  color  will  be  proportional  to  the  amount  of 
ferrous  salt  present.  In  other  words,  potassium  ferri- 
cyanide is  in  this  case  used  as  a  developer.  Where  the 
paper  has  been  protected  from  the  light,  the  materials  are 
unchanged.  The  picture  can  be  fixed  by  washing  away 
the  ferric  chloride  and  the  excess  of  potassium  ferri- 
cyanide. 

In  making  commercial  blue-print  paper  a  single  com- 
pound, ammonium  ferric  citrate,  serves  both  as  the  ferric 
salt  and  as  the  reducing  agent.  The  paper  is  coated  with 
a  mixture  of  this  salt  and  the  developer,  potassium  ferri- 
cyanide. Such  a  paper,  after  exposure,  is  both  developed 
and  fixed  by  simply  washing  with  water. 

SUMMARY 

Pure  iron  is  light  gray,  malleable,  ductile. 
Atomic  weight  56.     Valence  2  or  3.     Melting  point  1520°. 

Iron  corrodes  when  exposed  to  moist  air.  Red  hot  iron  decom- 
poses steam.  Iron  dissolves  in  dilute  hydrochloric  and  sulphuric 
acids  with  the  evolution  of  hydrogen  and  the  formation  of  a  ferrous 
salt. 

Iron  forms  two  series  of  salts.  Ferrous  salts  contain  iron  hav- 
ing a  valence  of  2,  and  ferric  salts  contain  iron  with  a  valence 
of  3. 

The  common  oxides  of  iron  are  ferric  oxide  (Fe2O3)  and  the 
magnetic  oxide  of  iron  (Fe3O4). 


382  IRON  AND  ITS   COMPOUNDS 

Ferric  oxide  pure,  or  impure  and  hydrated,  is  used  for  severa\ 
paint  pigments. 

Russia  iron  is  iron  coated  with  a  layer  of  the  magnetic  oxide 
of  iron. 

Ferric  hydroxide  is  formed  when  a  solution  of  a  base  is  added 
to  a  ferric  salt. 

Iron  rust  varies  in  composition,  but  may  be  considered  as  a 
double  compound  of  ferric  oxide  and  ferric  hydroxide.  Iron  is  pre- 
vented from  rusting  by  coating  it. with  paint,  enamel,  or  some 
metal  that  does  not  corrode  when  exposed  to  air.  Zinc,  tin,  and 
nickel  are  the  metals  most  commonly  used  for  this  purpose. 

Ferric  chloride  is  the  most  common  ferric  salt. 

Ferrous  sulphate,  green  vitriol,  is  the  most  common  ferrous  salt. 
It  is  used  in  the  manufacture  of  inks  and  paint  pigments. 

Yellow  prussiate  of  potash  is  potassium  ferrocyanide,  K4Fe(CN)6. 
Red  prussiate  of  potash  is  potassium  ferricyanide,  K3Fe(CN)6. 

Blue  prints  are  made  on  paper  coated  with  a  ferric  salt,  potas- 
sium ferricyanide,  and  a  reducing  agent. 

An  increase  in  the  valence  of  the  positive  part  of  the  molecule 
is  sometimes  termed  oxidation. 

A  decrease  in  the  valence  of  the  positive  part  of  the  molecule 
is  sometimes  termed  reduction. 

EXERCISES 

1.  Which  would  have  the  higher  melting  point,  pure  iron 
or  ordinary  wrought  iron  ?     What  principle  is  illustrated  by 
these  melting  points  ? 

2.  Is    pure  hydrogen   formed   when    hydrochloric    acid  is 
added  to  cast  iron  ?     Explain. 

3.  Is   ferrous    sulphate,   or   ferric   sulphate,   formed  when 
iron  is  treated  with  an  excess  of  sulphuric  acid  ? 


EXERCISES  383 

4.  How   would   you   convert   ferrous  chloride  into  ferric 
chloride  ?     Ferric  chloride  into  ferrous  chloride  ? 

5.  How  would  you  determine  whether  a  solution  contained 
a  ferric  or  a  ferrous  salt  ? 

6.  What  chemical  change  takes  place  when  ferrous  sul- 
phate is  calcined?     Mention  important  uses  of  the  chemical 
compound  that  constitutes  the  residue. 

7.  Why  is  it  difficult  to  keep  a  solution  of  ferrous  chlo- 
ride? 

8.  Which  oxide  of  iron  is  used  as  a  protective  coating  for 
iron  ?     Which  one  accelerates  the  rusting  of  iron  ? 

9.  Briefly  state  the  important  changes  that  take  place  dur- 
.  ing  the  making  of  a  blue  print. 

10.  Give  two  definitions  for  oxidation.     For  reduction. 

11.  Which  is  involved  in  the  conversion  of  ferrous  sulphate 
into  ferric  sulphate,  oxidation  or  reduction?     In  the  conver- 
sion of  potassium  ferrocyanide  into  potassium  f erricyanide  ? 

12.  Name  an  acid  suitable  for  removing  iron  rust  spots  from 
cotton  cloth. 

13.  Why  does  the  color  of  an  iron  ink  change  on  exposure 
to  air  ? 


CHAPTER   XXXII 
COPPER  AND  ITS  COMPOUNDS 

413.  Occurrence  and  Ores.  —  Copper  is  the  only  metal 
which  occurs  free  in  large,  widely  distributed  deposits. 
For  this  reason,  it  was  the  first  metal  extensively  used 
by  man.  The  copper  age  followed  the  stone  age.  The 
island  of  Cyprus  was  noted  in  the  time  of  the  Romans  for 
its  production  of  copper  or  Cyprian  brass.  We  obtain  the 
symbol  Cu  from  the  Latin  name,  cuprum. 


FIG.   124.  —  MASS   OF    NATIVE   COPPER    (3x2  ft.)   IN    THE    UNIVERSITY   OF 
MICHIGAN  MUSEUM. 

The  noted  mines  of  native  copper  in  Michigan,  along 
the  southern  shore  of  Lake  Superior,  were  extensively 
worked  before  Columbus  discovered  America.  From 
them  masses  of  copper  of  enormous  size,  one  of  which 

384 


ROASTING  OF  ORE  AND  PRODUCTION  OF  MATTE  385 

weighed  nearly  five  hundred  tons,  were  obtained.     These 
mines  are  still  an  important  source  of  copper. 

The  ores  of  copper  are  numerous,  and  many  of  them 
have  a  composition  represented  by  complex  formulas;  the 
more  important  ores  besides  native  copper  are  sulphides, 
oxides,  carbonates,  and  silicates.  Much  copper  is  obtained 
from  an  ore  named  chalcopyrite,  the  composition  of  which 
corresponds  approximately  to  the  formula  Ci^S  •  Fe2S3. 
Malachite,  a  basic  carbonate  of  copper,  CuCO3  •  Cu(OH)2, 
is  of  interest.  Polished  slabs  of  malachite  often  exhibit 
variegated  patterns  of  different  shades  of  green  which  are 
of  great  beauty,  and  the  mineral  is  highly  valued  for  orna- 
mental purposes. 

414.  Metallurgy ;  Steps  in  Process.  —  The  metallurgy  of 
copper  is  usually  complex ;   not  only  does  the  process  vary 
with  the  kind  of  ore  used,  but  similar  ores,  in  different 
localities,  are  seldom  treated  in  the  same  manner.     In  case 
the  ore  contains  much  ohalcopyrite,  the  process,  as  carried 
out  by  one  of  the  large  copper  companies,  consists   es- 
sentially in :  '. 

1.  Roasting  a  portion  of  the  ore  to  remove  sulphur. 

2.  The  production  of  a  complex  sulphide  called  matte. 

3.  Converting  the  matte  into  blister  copper. 

4.  Poling  the  blister  copper  and  casting  it  into  anode 
plates. 

5.  Refining  by  electrolysis. 

415.  Roasting  of  Ore  and  Production  of  Matte.  — When 
chalcopyrite,  Ci^S  •  Fe2S3,  is  roasted,  the  following  reac- 
tions probably  take  place : 

Fe2S3  +  4  02  — >-  2  FeQ  +  3  SO2 
2Cu2S  +  3O2— ^ 


386  COPPER   AND  ITS    COMPOUNDS 

The  roasted  ore  is  then  smelted  for  the  production  of 
matte,  in  a  blast  furnace,  similar  in  construction  to  the 
iron  blast  furnace  (§  392).  The  charge  for  the  furnace 
consists  of  the  roasted  ore,  a  certain  amount  of  unroasted 
(green)  ore,  and  coke.  The  ores  usually  contain  consider- 
able silica,  which  plays  an  important  part  in  the  action. 

The  copper  oxide  of  the  roasted  ore  reacts  in  the 
furnace  with  the  iron  sulphide  of  the  unroasted  ore  : 

3  Cu2O  +  FeaS8— >-  3  Cu2S  +  Fe2O3 

As  copper  has  a  greater  tendency  to  combine  with  sul- 
phur than  has  any  other  metal  present,  all  the  copper  is 
changed  to  sulphide.  A  part  of  the  iron  oxidizes  and 
unites  with  the  silica  which  is  present  in  the  ore  and 
forms  a  fusible  glassy  slag.  Some  of  the  iron  sulphide 
remains  with  the  cuprous  sulphide,  forming  the  matte, 
which  is  a  more  or  less  pure  mixture  of  cuprous  and 
ferrous  sulphides.  In  addition  to  the  sulphides  men- 
tioned, matte  contains  all  of  the  gold  and  silver  present  in 
the  ore,  and  generally  arsenic  and  antimony. 

The  matte  and  slag  are  run  into  a  shallow  tank  called 
a  forehearth,  where  the  lighter  slag  rises  to  the  top  and 
overflows  through  a  trough,  while  the  matte  collects  at 
the  bottom  and  is  from  time  to  time  drawn  off  through 
a  pipe.  Matte  contains  from  45  %  to  60  %  of  copper. 

416.  Conversion  of  Matte  to  Blister  Copper.  —  Matte  is 
converted  into  blister  copper  by  Bessemerizing,  in  a  fur- 
nace somewhat  similar  to  that  used  for  the  production  of 
Bessemer  steel  (Fig.  120).  The  matte  is  melted  and 
poured  into  the  converter ;  then  air  is  blown  through  the 
molten  mass  (Fig.  125).  Sulphur,  iron,  and  other  im- 
purities are  oxidized.  Those  oxides  which  are  volatile  are 
driven  off.  The  iron  oxide,  however,  unites  with  the 


POLING   OF  BLISTER    COPPER 


387 


quartz  of  the  furnace  lining  to  form  a  slag.     The  copper 
obtained  still  contains  all  of  the  gold  and  silver  present 
in  the  original  ore,  and  small 
quantities  of  other  impurities. 
Molten    copper    dissolves    con- 
siderable sulphur  dioxide,  which 
is  expelled  when  the  mass  cools, 
giving  the  copper  the  appear- 
ance  which    causes    it    to    be 
called  blister  copper. 

The  matte  is  often  converted 
to  blister  copper  by  heating  and 
melting  it  in  a  reverberatory 
furnace  similar  to  that  used  in 
the  next  operation,  and  allow- 
ing the  sulphur  to  be  oxidized 
by  the  air  passing  over  it. 


By  courtesy  of  The  Scientific  American. 

FIG.     125.  —  CONVERTER    IN 
OPERATION. 


417.   Poling  of  Blister  Copper  and  casting  of  Anode  Plates. 
-  Blister   copper  is   melted  in  a  reverberatory  furnace 


FIG.   126. — REVERBERATORY  FURNACE  FOR  POLING  COPPER. 


388 


COPPER  AND  ITS   COMPOUNDS 


(Fig.  126),  and  the  molten  mass  is  stirred  and  reduced 
by  the  gases  coming  from  a  long  pole  or  log  of  green  wood, 
which  is  forced  into  the  metal.  The  hydrocarbons  dis- 
tilled from  the  wood  unite  with  the  oxygen  combined  with 
the  copper.  This  process,  called  poling,  has  for  its  object 
the  reduction  of  the  small  amount  of  copper  oxide  that  is 
present  to  metallic  copper.  Any  one  who  has  seen  the 
interior  of  a  poling  furnace  in  operation  will  retain  a 
vivid  impression  of  the  seething  mass  of  molten  copper, 
dazzling  in  its  brilliancy  of  color.  After  being  poled,  the 
copper  is  cast  into  anode  plates  to  be  refined  by  elec- 
trolysis. 


By  courtesy  of  The  Sole  Uflc  Amertc  in. 

FIG.  127.  —  TANK-HOUSE  FOR  ELECTROLYTIC  COPPER  REFINING. 

418.  Refining  by  Electrolysis.  —  The  anode  plates  from 
the  poling  furnace  are  about  f  of  an  inch  thick,  3  feet 
wide,  and  3  feet  long.  The  cathode  plates  are  of  pure 
copper  about  -f^  of  an  inch  thick.  They  are  suspended 


ELECTROLYTIC  REFINING  389 

in  wooden  tanks  containing  a  warm  solution  of  copper 
sulphate  acidulated  with  sulphuric  acid  (Fig.  127).  Dur- 
ing the  electrolysis  the  solution  is  kept  slowly  circulat- 
ing, and  at  a  definite  concentration.  When  the  current 
passes,  pure  copper  is  deposited  on  the  cathode.  A  part 
of  the  impurities  enter  the  bath,  while  others,  including 
gold  and  silver,  fall  to  the  bottom  of  the  tank  and  form  a 
substance  known  as  mud.  The  gold  and  silver  are  recov- 
ered from  the  mud. 

The  cathode  plates  for  this  process  are  made  at  the  re- 
finery. Some  copper  refiners  do  not  use  pure  copper  cath- 
ode plates,  but  arrange  the  impure  plates  so  that  the  copper 
from  the  front  of  one  plate  is  deposited  on  the  back  of  the 
next  one. 

419.  Properties  of  Copper.  —  Copper  has  a  characteristic 
reddish  color.     Only  two  of  the  common  metals,  gold  and 
silver,  surpass  it  in  malleability  and  ductility.     It  stands 
next  to  silver  as  a  conductor  of  electricity. 

On  exposure  to  the  atmosphere,  copper  is  attacked  by 
carbon  dioxide  in  the  presence  of  moisture,  and  becomes 
covered  with  a  coating  of  a  basic  carbonate  of  a  greenish 
color.  The  coating,  once  formed,  adheres  to  the  copper 
underneath  and  protects  it.  Copper  is  readily  attacked 
by  nitric  acid  (preparation  of  nitric  oxide,  §  249),  but 
neither  dilute  hydrochloric  acid  nor  dilute  sulphuric  acid 
attack  it  in  the  absence  of  air.  It  is  readily  acted  upon 
by  hot,  concentrated  sulphuric  acid  (preparation  of  sul- 
phur dioxide,  §  206).  Boiling  concentrated  hydrochloric 
acid  slowly  converts  copper  into  cuprous  chloride,  CuCl. 

420.  Uses  of  Copper.  —  Large  quantities  of  copper  are 
used  for  a  great  variety  of  purposes.     Among  the  more 
important  may  be  mentioned  its  use  as  wire  and  cables 


390       COPPER  ANn  ITS  COMPOUNDS 

for  the  transmission  of  electric  currents ;  for  this  purpose 
it  must  be  practically  pure,  as  very  small  amounts  of  im- 
purity considerably  impair  the  conductivity.  If  the  con- 
ductivity of  pure  copper  is  considered  as  100,  copper  con- 
taining 0.8  %  of  arsenic  has  a  conductivity  of  only  30, 
and  copper  containing  0.5  %  of  silicon  has  a  conductivity 
of  28.  Other  uses  of  copper  include  its  employment  in 
the  manufacture  of  various  articles  for  domestic  and 
scientific  purposes,  such  as  water  heaters,  kettles,  stills, 
vacuum  pans,  etc.  Much  copper  is  also  employed  in  the 
manufacture  of  alloys.  Brass  is  an  alloy  of  copper  and 
zinc ;  bronze  is  an  alloy  of  copper  and  tin,  to  which  some- 
times zinc  and  other  metals  are  also  added  ;  German  silver 
is  an  alloy  of  copper,  nickel,  and  zinc ;  and  aluminum 
bronze  is  an  alloy  of  copper  and  aluminum. 

421.  Compounds  of  Copper.  —  Copper  forms  two  kinds  of 
ions,  cuprous,  Cu+,  and  cupric,  Cu++.     Its  valence  may 
therefore  be  considered  to  be  sometimes  one  and  at  other 
times  two.     The  univalent  cuprous  ion  unites  with  nega- 
tive ions  to  form  cuprous  compounds,  while  the  divalent 
cupric  ion  forms  cupric  compounds. 

Oxide  Sulphide  Chloride 

Cuprous      Cu2O  Cu2S  CuCl 

Cupric         CuO  CuS  CuCl2 

422.  Oxides  of  Copper.  —  Cuprous  oxide,  or  red  oxide  of 
copper,  Cu2O,  occurs  in  nature.     When  a  strip  of  copper 
is  heated  in  air,  a  layer  of  cuprous  oxide  may  be  found 
under  the  layer  of  black  cupric  oxide.     If  a  mixture  of 
cupric  oxide  and  charcoal  is  heated,  the  cupric  oxide  is 
first  reduced  to  cuprous  oxide,  and  then  the  cuprous  oxide 
is   reduced   to   copper.     Other   reducing   agents   have   a 


FEELING'S   TEST  FOR   SUGAR  391 

similar  effect  on  cupric  oxide.  The  formation  of  cuprous 
oxide  is  utilized  in  testing  for  glucose  by  means  of  Feh- 
ling's  solution.  Fehling's  solution  contains .  cupric  sul- 
phate, potassium  hydroxide,  and  Rochelle  salt.  When 
it  is  added  to  a  solution  containing  glucose,  or  a  similar 
reducing  agent,  and  the  mixture  is  boiled,  cuprous  oxide 
separates  as  a  red  precipitate.  The  Rochelle  salt  is  added 
to  prevent  the  formation  of  cupric  oxide,  which,  being 
black,  would  hide  the  color  of  the  cuprous  oxide.  Cuprous 
oxide  is  used  to  give  a  beautiful  red  color  to  pottery. 

Cupric  oxide,  or  black  oxide  of  copper,  CuO,  can  be  pre- 
pared by  heating  copper  in  air  and  also  by  heating  cupric 
hydroxide,  nitrate,  or  carbonate.  Many  compounds  con- 
taining hydrogen  are  oxidized  when  heated  with  cupric 
oxide,  the  hydrogen  being  converted  into  water.  If  car- 
bon is  present,  it  is  converted  into  carbon  dioxide.  These 
facts  make  cupric  oxide  a  valuable  substance  to  use  in  the 
determination  of  the  quantity  of  hydrogen  and  of  carbon 
present  in  compounds  containing  these  elements. 

423.  Preparation  of  Copper  Sulphate.  —  Crystallized  cop- 
per sulphate,  or  blue  vitriol,  CuSO4  •  5  H2O,  is  prepared  on 
a  large  scale  by  placing  coarse  copper  shot  in  a  perforated 
lead  basket,  and  then  causing  the  basket  and  contents  to 
move  up  and  down  so  that  they  will  at  one  time  be  in  the 
air  and  at  another  time  immersed  in  warm,  dilute  sul- 
phuric acid.  When  the  basket  enters  the  acid,  air  is  car- 
ried into  the  acid  with  the  shot.  The  action  of  the  acid 
on  the  copper  in  the  presence  of  air  results  in  the  for.ma- 
tion  of  copper  sulphate,  which  passes  into  solution  : 

2  Cu  +  02  +  2  H2S04  — -^2  CuS04  +  2  H2O 

The  solution,  after  being  sufficiently  concentrated,  is 
allowed  to  stand  in  lead-lined  vats  in  which  are  suspended 


392 


COPPER   AND  ITS   COMPOUNDS 


lead  strips.     Blue  vitriol  crystallizes  on  the  lead  and  is 
purified  by  recrystallization. 

Blue  vitriol  is  also  obtained  as  a  by-product  in  one 
method  used  in  separating  gold  from  silver.  The  melted 
alloy  of  these  two  metals  is  granulated  by  pouring  it  into 
cold  water.  The  granulated  mass  is  boiled  with  concen- 
trated sulphuric  acid  until  the  silver  is  dissolved  as  silver 
sulphate.  The  gold  remains  undissolved  and  settles  to 
the  bottom  of  the  vat.  The  solution  of  silver  sulphate  is 
removed  to  lead-lined  vats  and  the  silver  separated  by  the 
addition  of  copper: 

Ag2SO4  +  Cu  —  ^.  CuSO4  +  2  Ag 


FIG.    128. — COPPER  SULPHATE  CRYSTALS. 

424.  Properties  and  Uses  of  Copper  Sulphate.  —  Copper 
sulphate  forms  deep  blue  crystals  (Fig.  128)  which  efflo- 
resce in  dry  air.  Its  water  solution  gives  an  acid  reaction 
with  litmus  (§  183). 

For  some  time  the  great  value  of  copper  sulphate  as  a 
fungicide  has  been  recognized.  A  mixture  of  copper  sul- 
phate and  slaked  lime,  known  as  the  Bordeaux  mixture, 
is  now  extensively  employed  for  this  purpose.  A  thick 
paste  of  calcium  hydroxide  and  copper  sulphate  was  first 


USES  OF  COPPER  SULPHATE        393 

used  near  the  city  of  Medoc,  France,  to  keep  boys  from 
stealing  grapes.  When  placed  upon  the  trellises  and  vines 
it  was  conspicuous,  and  was  believed  to  be  poisonous.  In 
1882,  Millardet,  professor  of  botany  in  Bordeaux,  visited 
the  vineyards  near  Medoc,  and  was  informed  by  the  grape 
growers  that  those  portions  of  the  vineyard  which  had 
been  treated  with  the  paste  were  not  attacked  with  mildew. 
Much  work  has  been  done  in  the  United  States  Department 
of  Agriculture  in  determining  the  value  of  the  Bordeaux 
mixture  as  a  general  fungicide.  Its  use  in  this  country 
has  saved  crops  worth  many  thousands  of  dollars. 

Dilute  solutions  of  copper  sulphate  are  used  to  moisten 
seeds  of  cereals  prior  to  sowing,  to  prevent  the  attack  of 
fungi  called  smuts. 

Plants  known  as  algae  grow  abundantly  in  the  water  of 
ponds  and  reservoirs.  Some  of  them  impart  to  the  water 
disagreeable  odors;  others  produce  effects  equally  unde- 
sirable. Copper  sulphate  is  added  to  the  water  of  ponds 
thus  affected,  in  the  proportion  of  one  part  of  copper  sul- 
phate to  from  one  to  eight  million  parts  of  water,  for  the 
purpose  of  destroying  algae.  The  solution  is  too  dilute  to 
kill  fish.  The  copper  sulphate  appears  to  react  with  the 
albumen  of  the  algae  to  form  an  insoluble  substance  which 
sinks  to  the  bottom  of  the  ponds. 

Copper  sulphate  has  many  other  important  uses.  •  It  is 
employed  in  batteries,  in  electroplating,  as  a  mordant  in 
dyeing,  and  for  making  other  compounds  of  copper. 

SUMMARY 

The  atomic  weight  of  copper  is  63.6.  Specific  gravity  8.9. 
Melting  point  1083°  C. 

Copper  occurs  as  metal ;  this  and  the  sulphides  are  its  principal 
sources. 


394  COPPER   AND  ITS   COMPOUNDS 

It  is  separated  from  its  ores  by  burning  out  the  sulphur  and  re- 
ducing the  oxide  by  carbon.  It  is  purified  by  electrolysis. 

Copper  is  durable  under  ordinary  atmospheric  conditions,  and 
is  used  for  protective  coverings.  Being  ductile  and  a  good  con- 
ductor, it  is  used  for  electric  conductors.  As  a  constituent  of 
many  alloys,  copper  finds  wide  use. 

Copper  sulphate  is  the  most  important  compound  of  copper.  It 
is  used  as  a  fungicide,  for  paints,  for  plating,  and  in  some  batteries. 

EXERCISES 

1.  What  metals  are  usually  found  associated  with  copper  ? 

2.  How  is  iron  separated  from  copper?     How  is  silver? 

3.  Heavy  electric  cables  of  copper  often  have  iron  wire 
above  them  to  which  they  are  fastened.     Why  ? 

4.  What  is  the  result  of  the  action  of  atmospheric  agents 
on  copper  ? 

5.  What  volume  of  nitric  oxide  will  be  produced  by  the 
action  of  10  grams  of  copper  with  nitric  acid  ? 

6.  How  could  you  tell  whether  a  given  substance  was  gilt 
(brass)  or  gold  ? 

7.  What  is  the  most  important  use  of  copper  ?     How  does 
its  purity  affect  its  fitness  for  this  purpose  ? 

8.  Name  three  alloys  of  copper  and  their  constituents. 

9.  What  copper  compound  is  used  in  pottery  and  in  glass  ? 
Why? 

10.  What  would  be  obtained  if  ammonia  were  passed  over 
heated  copper  oxide  ? 

11.  How   much  blue   vitriol  could  be  obtained,  using  one 
ounce  of  copper  ? 

12.  Write   the   equation   for   the   change  that  takes  place 
when  a  strip  of  copper  is  placed  in  a  solution  of  silver  nitrate. 


EXERCISES  395 

13.  How  much  copper  could  be  obtained  from  one  ounce  of 
blue  vitriol  ? 

14.  One  gram  of  silver  is  obtained  by  the  decomposition  of 
its  sulphate  by  copper.     What  weight  of  copper  passes  into 
solution  ? 

15.  Calculate  the  percentage  of  water  of  crystallization  in 
crystalline  copper  sulphate,  CuS04  •  5  H2O. 

16.  State  two  uses  for  copper  sulphate. 

17.  How  could  you  tell  whether  or  not  a  given  substance  is 
a  compound  of  copper  ? 

18.  Outline  the  process  by  which  a  vessel  might  be  copper 
plated. 


CHAPTER   XXXIII 
SILVER,  GOLD,  AND  PLATINUM 

SILVER 

425.  Occurrence.  —  Silver  is  the  most  common   of   the 
precious  metals.     Silver  has  been  known  from  the  earliest 
times,  as  it  frequently  occurs  free  in  rocks  and  is  easily 
separated. 

Native  silver  is  found  in  Arizona,  Mexico,  South  Amer- 
ica, and  elsewhere,  but  much  of  the  silver  now  used  is 
obtained  from  sulphide  ores,  usually  associated  with  lead, 
copper,  arsenic,  and  gold.  Silver  chloride  (horn  silver) 
occurs  in  nature,  and  traces  of  silver  compounds  are  found 
in  sea  water.  The  principal  supply  of  silver  is  from 
Mexico,  United  States,  Canada,  Australia,  and  Peru. 

426,  Metallurgy.  —  Some   of  the  ores  of  silver  are  so 
complex  that  various  processes  are  employed  in  the  sepa- 
ration of  the  metal,  but  since  so  large  a  proportion  of  the 
commercial  metal  is  obtained  from  lead  ores,  only  the 
method  used  for  these  (Parkes'  process)  will  be  described. 

The  ore,  largely  lead  sulphide,  is  roasted  to  remove 
sulphur,  and  then  reduced  as  described  under  the  metal- 
lurgy of  lead  (§  471).  The  crude  metal  thus  obtained  is 
heated  in  a  reverberatory  furnace  and  stirred.  Such 
metals  as  copper,  antimony,  and  arsenic  are  oxidized, 
forming  a  scum  on  the  surface  of  the  lead,  and  this  is 
skimmed  off.  The  molten  metal  is  now  run  into  iron  pots 
and  a  small  percentage  of  zinc  is  stirred  into  it.  As  the 


METALLURGY  OF  SILVER 


397 


mixture  cools,  an  alloy  of  zinc  with  silver  and  gold  comes 
to  the  top  and  is  skimmed  off,  but  little  of  the  lead  being 
removed.  If  there  is  much  silver  in  the  crude  lead,  the 
treatment  with  zinc  may  be  repeated. 

The  skimmings  containing  zinc,  lead,  silver,  and  gold 
are  now  heated  in  a  retort  and  the  zinc  removed  by 
distillation. 

The  residue,  containing  lead,  silver,  and  gold,  is  then 
cupelled,  that  is,  heated  in  a  bone-ash  dish  in  a  shallow 
furnace  exposed  to  the  air.     The  lead  oxidizes,  and  the 
melted  lead  oxide  flows  off  and  is  re- 
covered.    The  melted  silver  and  gold 
that  remains  is  then  poured  into  molds. 
A  small  cupellation  furnace  is  shown 
in  Fig.   129  ;    a  is  a  muffle  and  b  the 
cupel  in  which  the  silver  and  gold  is 
finally  left  as  a  metallic  button. 

The  gold  is  separated  from  the  silver 
by  treating  the  alloy  with  hot  concen- 
trated sulphuric  acid  or  nitric  acid. 
The  silver  dissolves  as  the  sulphate  or  the 
nitrate,  but  the  gold  is  not  affected,  and 
after  washing  is  melted  and  cast  into  bars. 

The  silver  is  recovered  from  the  solution  by  hanging  in 
it  plates  of  copper  : 

2  AgNO,  +  Cu  — •»-  Cu(NO3)2  +  2  Ag 

The  silver  is  deposited  in  a  fine  crystalline  form  known  as 
cement  silver.  The  "  silver  tree  "  (Fig.  130)  is  produced 
in  this  way. 

Another  method  of  separating  gold  from  silver  is  by 
electrolysis.  The  alloy  is  made  the  anode  in  a  dilute 
nitric  acid  solution  of  silver  nitrate,  the  anode  sheet  being 
inclosed  in  a  canvas  bag.  With  a  current  of  low  voltage, 


FIG.  129. 


398 


SILVER,    GOLD,  AND  PLATINUM 


silver  is  dissolved  from  the  anode  as  the  nitrate  and  rede- 
posited  on  the  cathode  as  practically  pure  metal.  The 
gold  is  unaffected  and  remains  at  the  anode,  and  as  the 
anode  disintegrates,  collects  as  a  mud  in  the  canvas  bag. 

427.  Physical  Properties.  —  Silver  is  a  white  metal, 
fairly  hard,  capable  of  receiving  and  retaining  a  high  pol- 
ish. It  is  the  best  conductor  of  heat  and  of  electricity. 

Being  ductile  and  malleable, 
it  is  readily  worked  into  articles 
of  various  shapes. 

428.   Chemical     Properties.  — 

Silver  does  not  change  in  pure 
air  and  does  not  oxidize  on 
being  heated.  It  darkens  read- 
ily in  the  presence  of  sulphur 
compounds,  showing  such  stains 
as  are  seen  on  silver  spoons  that 
have  been  used  with  eggs  or 
mustard,  on  coins  carried  in 
the  pocket,  or  on  silverware 
about  the  house.  "  Oxidized  " 
silver  owes  its  color  to  a  thin 

coating  of  silver  sulphide,  produced  by  dipping  the 
metal  in  a  solution  of  crude  potassium  sulphide. 

Alkalies  do  not  affect  silver.  Nitric  and  sulphuric 
acids  react  with  it  as  they  do  with  copper : 


FIG.  130.  —  SILVER  TREE. 


3Ag 


2H2S04 
4HN0 


Ag2S04 
3AgNO3 


S0 


429.  Cleaning  Silverware.  —  The  tarnish  may  be  removed 
from  silver  by  rubbing  with  a  very  fine  abrasive,  like 
diatomaceous  earth  (electrosilicon),  or  by  dissolving  it 


CLEANING  SILVER  399 

chemically.  Moistening  a  dry  silver  polish  with  ammonia 
aids  its  action,  on  account  of  the  solvent  power  of  the 
ammonia.  The  cyanide  solution  used  by  jewelers  should 
never  be  employed  in  the  home,  as  it  is  one  of  the  most 
deadly  poisons  known. 

Re.cently  a  •  simple  and  very  satisfactory  method  of 
cleaning  silverware  by  boiling  it  with  water  in  an  alumi- 
num dish,  has  been  devised.  In  this  case,  aluminum 
replaces  the  silver  in  the  compounds  forming  the  tarnish. 
In  cleaning  plated  silver,  the  fact  that  the  plating  is 
pure  silver  and  is,  therefore,  softer  than  ordinary  sterling 
or  coin  silver  should  be  kept  in  mind.  Plated  silver 
should  never  be  rubbed  hard  with  abrasive  polishes,  even 
those  which  might  be  suitable  for  solid  silver. 

430.  Uses  of  Silver. — Since  .pure    silver    is   not  hard 
enough  to  stand  the  wear  and  tear  of  constant  use,  it  is 
alloyed   with   other   metals,    for   instance   copper.       The 
silver  coins  of  the  United  States  contain  90%  of  silver 
and  are  said  to  be  900  tine.     British  coins  are  925  fine 
(92.5%  silver),  and  this  is  the  grade  known  as  sterling 
silver.      On  account  of  its  color,  durability,  and  luster 
silver  has  long  been  used  for  jewelry  and  ornaments,  and 
as  a  plating  on  cheaper  metals. 

Mirrors  are  made  by  depositing  a  layer  of  silver  on 
polished  glass.  A  solution  of  silver  nitrate  to  which 
has  been  added  some  ammonia  and  a  reducing  agent,  as 
formaldehyde  or  grape  sugar,  is  flowed  over  the  glass  and 
gently  warmed.  The  silver  is  reduced  and  deposited  as  a 
bright  film  on  the  glass.  This  is  washed,  dried,  and 
.varnished  to  protect  it. 

431.  Silver  Plating  is  usually  done  by  electrolysis.     To 
secure  a  firm,  uniform  deposit,  the  electrolyte  is  a  solution 


400  SILVER,   GOLD,  AND  PLATINUM 

of  silver  and  potassium  cyanides  (Fig.  131,  b)  made  by 
adding  potassium  cyanide  solution  to  a  solution  of  silver 
nitrate  until  the  precipitated  silver  cyanide  is  dissolved. 
A  bar  or  sheet  of  silver  is  used  as  the  anode  (a)  and 

the  object  to  be  plated  as  the 
cathode  (<?),  a  rather  weak  cur- 
rent being  employed.  The  posi- 
tive silver  ions  are  discharged 
and  deposited  on  the  cathode. 
The  negative  cyanide  ions,  dis- 
charged on  the  anode,  combine 
with  the  silver,  forming  silver 

cyanide.  This,  on  dissolving,  is 
FIG.  131.  —  SILVER  PLATING.  J.  _. 

dissociated.  Ihe  amount  of  sil- 
ver in  the  solution  is  unchanged,  for  silver  is  dissolved 
from  the  anode  and  deposited  on  the  cathode. 

432.  Compounds  of  Silver.  — Silver  nitrate,  AgNO3,  is  the 
most  common  compound.  It  is  prepared  by  dissolving 
silver  in  nitric  acid: 

3  Ag  +  4  HNO3  — >-  3  AgNO3  +  2  H2O  +  NO 

It  is  very  soluble  in  water  and  crystallizes  from  it  in  flat, 
rhomboidal,  transparent  crystals.  In  contact  with  organic 
matter  and  exposed  to  the  light,  it  darkens.  Molded 
into  sticks,  silver  nitrate  is  used  as  a  cauterizing  agent  for 
warts,  wounds,  and  sores,  and  is  known  as  lunar  caustic. 
Silver  nitrate  is  the  most  important  compound  of  silver 
because  most  of  the  other  silver  compounds  are  made 
from  it. 

Silver  chloride,  AgCl,  is  made  by  adding  a  solution  of  a. 
chloride  to  a  solution  of  a  silver  salt  : 

AgNO3  +  KC1  — +-  AgCl  +  KNO3 


PHOTOGRAPHY  401 

The  silver  chloride  separates  as  a  white,  curdy,  insoluble 
solid.  Silver  chloride  does  not  dissolve  in  acids,  but  dis- 
solves in  ammonia  and  in  sodium  thiosulphate,  the  hypo 
of  the  photographer. 

Silver  bromide,  AgBr,  and  silver  iodide,  Agl,  resemble 
the  chloride;  they  have  a  yellowish  tinge,  are  more  easily 
changed  in  the  light,  and  are  less  soluble.  Like  the 
chloride,  they  are  extensively  used  in  photography. 

PHOTOGRAPHY 

The  preparation  of  the  photographic  negative  involves 
these  processes:  the  exposure,  the  development,  the  fixing, 
and  the  washing. 

433.  Exposure.  —  The    photographic    plate   consists   of 
glass  or  transparent  celluloid  coated  with  a  film  of  gelatine 
containing  very  finely  divided  silver  bromide,  which,  as 
has   been  stated,  is  sensitive  to  light  in  that  it  becomes 
somewhat  less  soluble  and  more   easily  reduced.     In  the 
camera  the  plate  is  exposed  to  light,  and  the  change  in 
the  silver  bromide  is  produced,  strongly  where  the  light 
is  bright,  less  intensely  in  the  shadows.     The  exposure  is 
very  short  in  the  camera,  and  produces  no  visible  change 
in  the  plate. 

434.  Developing.  —  The    next   operation   is   to   develop 
the  picture.     As  the  exposed  silver  compound  is  a  little 
more  easily  affected  than  the  unexposed  compound,  it  is 
possible  to  change  the  one  without  materially  affecting 
the  other.     For  this,  the  developer  is  used.      The  developer 
is  a  reducing  agent  of  such  strength  that  it  is  capable  of  con- 
tinuing the  change  begun  by  the  light,  but  is  not  capable  of 
initiating  the  change  in  the  unaffected  parts  of  the  plate. 


402  SILVER,    GOLD,  AND  PLATINUM 

Ferrous  sulphate,  pyrogallol,  hydroquinone,  and  many 
other  reducing  agents  are  used  as  developers. 

2  AgBr  +  H2O  — ^  2  Ag  +  2  HBr  +  O 

The  acid  is  neutralized  by  the  alkali  added  in  the  devel- 
oper, and  the  oxygen  is  removed  by  the  reducing  agent. 
Where  the  plate  has  been  exposed  to  the  light,  there  will 
be  a  deposit  of  silver,  which  appears  dark  because  it  is 
very  finely  divided.  Where  no  light  acted,  the  silver 
compound  is  unchanged. 

435.  Fixing.  —  When   it   is   seen   that    the    picture   is 
developed   sufficiently,   it   is   placed   in   the  fixing   bath. 
This  is  a  solution  of  sodium  thiosulphate,  Na2S2O3,  com- 
monly called  hyposulphite  of  soda,  and  is  capable  of  dis- 
solving many  silver  compounds,  such  as  the  silver  bromide, 
which  remains  unreduced  in  those  parts  of  the   picture 
where  the  light  has  acted  least.     This  unchanged  silver 
bromide   is   dissolved,   and   the    glass    remains    clear    in 
these  places.     As  all  the  material  sensitive  to  light  has 
been  removed,  the  plate  is  said  to  be  fixed ;   it    is   then 
thoroughly  washed  and  dried. 

On  the  fixed  plate,  those  parts  of  the  scene  which  are 
brightest,  that  is,  those  parts  which  are  white  or  blue,  are 
represented  by  a  dark  deposit  of  silver;  the  dark  parts  of 
the  scene  are  clear,  so  that  shades  are  reversed;  hence  it 
is  called  a  negative  (Fig.  132,  6). 

436.  Printing    and    Toning.  —  The    finished    picture  on 
paper  is  made  from  the  negative.     The  paper  is  sensitized, 
as  was  the  plate,  by  a  film  of  silver  chloride  or  bromide. 
It  is  exposed  to  the  light  under  the  negative.     Now  those 
parts  of  the  paper  under  the  clear  parts  of  the  negative 
will  be  affected  most  by  the  light  and  will  be  the  darkest 


PRINTING  AND   TONING 


403 


on  reduction ;  the  parts  under  the  heavy  deposits  will  be 
little  affected  and  appear  light,  as  they  do  in  the  object, 
so  that  the  print,  being  the  reverse  of  the  negative,  is  a 
positive  (Fig.  132,  a).  Its  shades  agree  with  those  of  the 
object. 

The  positive  is  developed  in  the  same  manner  as  the 
negative  in  most  cases,  but  in  printing  out  papers,  the 
developer  is  in  the  paper,  so  that  the  reduction  occurs 


\ 


a,  POSITIVE. 


b,  NEGATIVE. 


FIG.   132. 


and  the  picture  appears  during  the  exposure.  The  print 
is  fixed  and  washed  as  the  plate  was,  and  to  render  it 
more  permanent  and  to  improve  the  color,  the  print  is 
toned  by  immersing  it  in  a  solution  of  gold  chloride,  so 
that  some  of  the  silver  of  which  the  picture  is  composed 
is  replaced  by  gold,  giving  it  a  warmer  tone.  Platinum 
and  lead  compounds  are  also  used  in  toning.  A  tintype 
is  a  whitened  negative  on  a  polished  black  surface.  Other 
materials  might  be  used  besides  silver  compounds,  but 
these  are  the  most  sensitive  to  slight  variations  in  light 


404  SILVER,    GOLD,  AND  PLATINUM 

and  are  the  most  easily  controlled.     The  blue  print  process 
is  described  in  §  412. 

GOLD 

437.  Occurrence.  —  Gold    has    been    known    from    the 
earliest   times.     At   present   the  principal  supply  comes 
from  Africa,  the  United  States,  and  Australia.     It  com- 
monly occurs  native,  or   alloyed  with   silver   and   other 
metals.     It  also  occurs  combined  with  tellurium,  an  ele- 
ment closely  related  to  sulphur.     Native  gold  is  found  in 
veins  running  through  quartz  rock  and  also  in  the  beds  of 
streams  whose  sands  have  been  formed  from  the  disinte- 
gration of  such  gold-bearing  quartz.     It  often  occurs  'in 
nuggets  varying  in  size  from  that  of  a  tiny  pebble  toj  a 
mass  weighing  over  a  hundred  pounds. 

438.  Separation.  —  From  river  sands  and  gravel  gold  is 
separated    by   washing   with   water.     The    lighter   rock 
particles  are  washed  off,  leaving  the  gold.     Partially  dis- 
integrated rock  and  coarse  gravels  are  sometimes  mined 
by  dredging,  crushing  and  washing  them  with  streams  of 
water   through   troughs,  with    transverse   cleats  holding 
mercury  along  the  bottom.      These  retain  the  heavy  gold 
and  permit  the  soil  and  gravel  to  be  swept  on. 

439.  Metallurgy.  —  When  gold  occurs  in  veins  in  mas- 
sive rock,  the  rock  is  blasted  with  dynamite.     The  broken 
rock  is  crushed  to  small  pieces  by  powerful  iron  crushers 
and   is   then   pounded   into   fine   powder  by  heavy  iron 
stamps  working  in  iron  troughs.     Water  is  kept  flowing 
through  these  troughs,  and  the  gold  and  rock  leave  them 
as  a  thin  mud.     This  is  caused  to  flow  over  silver-plated 
copper  plates  coated  with  mercury.     The  mercury  amal- 
gamates with  the  gold,  and  when  a  sufficient   quantity 


USES  OF  GOLD  '  405 

accumulates,  the  amalgam  is  scraped  off  the  plates  and 
freed  from  mercury  by  distillation. 

The  gold  that  escapes  amalgamation  is  extracted  by 
means  of  sodium  cyanide.  The  mud  is  allowed  to  stand 
in  a  weak  solution  of  cyanide  exposed  to  air  for  days 
or  weeks  and  a  double  cyanide  of  gold  and  sodium  is 
formed.  The  gold  is  precipitated  from  this  solution  by 
zinc  or  is  extracted  by  electrolysis.  This  cyanide  process 
is  also  applied  directly  to  ores  poor  in  gold  and  to  tellu- 
rides.  Its  use  in  this  country  is  increasing. 

The  separation  of  gold  from  copper  slimes  has  already 
been  mentioned  (§  418). 

440.  Properties.  —  Gold  is  soft  and  heavy  and  is  the  most 
malleable  and  ductile  of  metals.     The  presence  of  a  small 
amount  of  other  metals,  however,  often  makes  it  brittle. 
Gold  leaf  has  been  made  2  5  ^0  6  0  of  an  inch  thick.     Gold 
leaf  transmits  green  light,  while  finely  divided  gold,  when 
suspended  in  liquids,  appears  purple  by  reflected   light, 
and   blue   by  transmitted   light.     Gold   in   this   form  is 
known  as  colloidal  gold. 

Gold  is  unaffected  by  air  or  water  at  any  temperature. 
Ordinary  acids  do  not  act  on  it,  but  it  is  dissolved  by 
aqua  regia,  with  the  formation  of  auric  chloride,  AuCl3. 

441.  Uses.  —  Pure  gold  is  used  as  gold  leaf.     The  metal 
is  too  soft   to   be  used  alone  for  other   purposes  and  is 
alloyed  with  silver  or  copper.     The  proportion  of  gold  is 
always  indicated  by  the  number  of  carats  fineness :  pure 
gold  is  24  carats  fine,  18-carat  gold  contains  18  parts  by 
weight  of  gold  and  6   parts  of  other  metal.     This  carat 
should  be  distinguished  from  ths  carat  used  in  weighing 
gems,  which  has  recently  been  standardized  at  a  weight  of 
200  milligrams.     The  gold  coins  of  the  United  States  are 


406'  SILVER,   GOLD,  AND  PLATINUM 

90  %  gold  and  10  %  copper.  Articles  are  gold  plated  by 
an  electroplating  process  with  a  bath  of  double  cyanide  of 
gold  and  potassium. 

COLLOIDS 

442.  Nature.  —  The  finely  divided  gold  mentioned  in 
§  440  is  an  example  of  a  large  class  of  substances  known 
as  colloids.     Colloids  form  suspensions  with  liquids,  in 
which  the  colloid  is  as  uniformly  distributed  through  the 
liquid  as  a  dissolved  substance  is  in  its  solvent.     These 
colloidal  suspensions  can  often  be  filtered  without  change 
and  the  colloids  do  not  settle  out  of  the  suspension  on 
standing.       Ordinary   soluble    substances,     such   as    the 
soluble  acids,  bases,  and  salts,  are  sometimes  called  crys- 
talloids, as  most  of  them  form  crystals  when  the  water  in 
which  they  are  dissolved  is  evaporated.     If  a  mixture  of 
a  crystalloid  solution  and  a  colloidal  suspension  be  placed 
in  an  animal  or  vegetable  membrane  and  immersed  in  run- 
ning water,  the  crystalloid  will  eventually  be  all  washed 
out,  while  the  colloid  will  not  leave  the  membranous  bag. 
Such  a  membrane  is  called  a  dialyzing  membrane.     In  a 
solution  of  a  crystalloid,  we  have  assumed  that  the  crys- 
talloid was  divided  into  particles  usually  smaller  than  the 
molecules  (§  148) ;    such  particles   will  pass   through  a 
dialyzing  membrane.     Evidently  the  particles  of  a  colloid 
are  much  larger,  as  they  cannot  pass  through  the  pores  of 
such  a  membrane.     A  colloid,  then,   is  a  substance  which 
forms   uniform    permanent  suspensions   with    liquids,   and 
whose  particles  cannot  pass  through  a  dialyzing  membrane. 
Colloids  affect  very  little  the  boiling  point  and  the  freez- 
ing point  of  the  liquid  in  which  they  are  suspended. 

443.  Production.  —  Colloids  are  produced  in  a  number  of 
ways.     Colloidal  gold,  silver,  copper,  or  platinum  may  be 


PRODUCTION  OF  COLLOIDS  407 

obtained  by  establishing  an  electric  arc  between  wires  of 
one  of  these  metals  beneath  the  surface  of  very  pure  water. 
They  may  also'  be  obtained  by  chemical  reactions  carried 
out  under  very  restricted  conditions.  These  colloidal  sus- 
pensions of  metals  show  a  considerable  variety  of  color,  ac- 
cording to  the  conditions  under  which  they  are  prepared. 

444.  Importance.  —  The  practical  importance  of  colloids 
is  enormous.     A  great  number  of  common  substances, 
such  as  gelatine,  glue,  starch,  leather,  paper,  and  rubber, 
are  natural  or  artificial  colloids.      Fertile  soil   must  be 
largely  in  a  colloidal  condition  in  order  that  moisture  and 
the  nutriment  from  fertilizing  material  may  be  adsorbed, 
that  is,  condensed  on  the  surface  of  its  particles.     The  cell 
walls  of  the  tissues  of  the  body  are  dialyzing  membranes, 
through  which  colloids  cannot  pass,  and  the  processes  of 
nutrition  largely  depend  upon  the  formation  of  colloids 
at  the  right  time  and  place.     Glass  is  colored  by  making 
colloidal  suspensions  of  metals  in  the  melted  glass ;  ruby 
glass  is  colored  with  colloidal  gold. 

PLATINUM 

445.  Occurrence.  —  Platinum  occurs  native,  alloyed  with 
osmium  and  iridium,  which  closely  resemble  it,  and  with 
other  metals.     The  most  important  deposits  of  platinum 
are  in  the  Ural  Mountains ;  it  is  also  found  in  California, 
Australia,   and   a   few  other   places.     The  separation  of 
platinum  from  the  metals  alloyed  with  it  is  a  complicated 
process. 

446.  Properties.  —  Platinum  is  a  white,  lustrous  metal, 
about  twice  as  heavy  as   lead.     It  is  very  malleable  and 
ductile  and  is  infusible  except  in  the  oxyhydrogen  flame 
or  the  electric  arc.     The  metal  is  permeated  by  or  occludes 


408  SILVER,  GOLD,  AND  PLATINUM 

large  quantities  of  hydrogen  when  cold,  with  an  increase  in 
temperature,  and  releases  the  hydrogen  when  ignited.  It 
does  not  take  up  oxygen  when  hot,  but  condenses  it  on  the 
surface  when  cold.  Platinum  may  be  obtained  as  a  fine 
black  powder,  platinum  black,  by  the  action  of  a  reducing 
agent  on  a  solution  of  one  of  its  salts  and  as  a  spongy 
platinum  by  igniting  the  double  chloride  of  platinum  and 
ammonium.  When  platinum  is  to  be  used  as  a  catalytic 
agent;  these  forms  produce  a  maximum  effect  for  the 
money  invested,  on  account  of  the  large  surface  they  pos- 
sess in  proportion  to  their  mass. 

Platinum  is  not  attacked  by  air  or  water  at  any  tem- 
perature, and  is  not  affected  by  acids,  except  aqua  regia. 
Caustic  alkalies,  phosphorus,  silicon,  and  carbon  attack  it 
when  hot,  so  none  of  these  substances  should  be  heated 
in  platinum  vessels.  Platinum  should  never  be  heated  in 
a  smoky  flame,  on  account  of  its  tendency  to  form  a  car- 
bide, nor  should  metals  be  heated  in  platinum  vessels. 

447.  Uses.  —  The  infusibility  of  platinum  and  its  chem- 
ical indifference  toward  the  great  majority  of  elements 
and  compounds  render  it  invaluable  in  chemical  opera- 
tions. It  finds  extensive  use  in  the  laboratory,  in  the  form 
of  dishes,  wire,  and  foil.  On  account  of  its  cost,  which  is 
more  than  that  of  gold,  it  is  used  only  to  a  limited  extent 
in  chemical  manufactures.  The  great  expense,  however, 
is  partly  compensated  for  by  its  indestructibility.  It  is 
used  for  pans  for  the  concentration  of  sulphuric  acid,  and 
large  quantities  of  platinum  black  are  employed  as  a 
catalytic  agent  in  the  manufacture  of  sulphuric  acid  by 
the  contact  process.  It  is  a  good  conductor  of  electricity 
and  expands  with  heat  at  the  same  rate  as  glass.  On  ac- 
count of  these  properties  it  is  sometimes  used  to  connect 
the  filaments  of  incandescent  lamps  with  the  wires  out- 


COMPOUNDS  OF  PLATINUM  409 

side  the  bulbs.  The  power  of  platinum  to  cause  the 
ignition  of  inflammable  gases  mixed  with  air  is  utilized  in 
self-lighting  burners  and  mantles.  Its  alloy  with  iridium 
is  hard  and  unalterable  in  air  and  is  used  for  the  manu- 
facture of  government  standards  of  length.  A  consider- 
able amount  of  platinum  is  used  in  settings  for  jewels. 
This  is  unfortunate,  as  much  platinum  needed  for  indus- 
trial operations  is  thus  withdrawn  from  the  market. 

448.  Compounds  of  Platinum.  —  The  most  important 
platinum  compound  is  Morplatinic  acid,  H2PtCl6,  which 
is  formed  by  dissolving  platinum  in  aqua  regia.  This 
forms  chlorplatinates  with  metallic  compounds.  It  is  used 
in  toning  platinum  photographs  and  as  a  test  for  potas- 
sium compounds.  The  test  depends  upon  the  fact  that 
potassium  chlorplatinate  is  but  slightly  soluble  in  water 
or  alcohol,  white  the  corresponding  sodium  compound  is 
decidedly  soluble. 

SUMMARY 

Silver  occurs  native,  and  with  other  metals  in  complex  sulphides 
and  as  the  chloride. 

It  is  extracted  from  lead  bullion  by  means  of  zinc,  and  purified 
by  electrolysis  or  treatment  with  acid. 

Silver  has  a  specific  gravity  of  10.5.  Atomic  weight  108. 
Melting  point  96 1  °.  It  is  the  best  conductor  of  heat  and  electricity. 

Silver  is  unaltered  by  pure  air,  but  is  tarnished  by  sulphur  com- 
pounds. 

Silver  is  alloyed  with  copper  for  most  uses.  A  double  cyanide 
of  potassium  and  silver  is  used  for  electroplating. 

Silver  nitrate  is  made  by  dissolving  silver  in  nitric  acid.  It  is 
the  basis  of  other  silver  compounds. 


410  SILVER,    GOLD,  AND   PLATINUM 

The  silver  halides  are  insoluble  compounds,  and  are  made  more 
easily  reducible  by  the  action  'of  light.  Photographic  plates  are 
coated  with  silver  bromide,  which,  after  exposure  to  the  light,  can 
be  reduced  by  a  developer.  The  unreduced  silver  bromide  is 
dissolved  by  sodium  thiosulphate.  , 

Prints  are  made  by  exposing  to  light,  under  the  negative,  paper 
coated  with  silver  bromide  or  chloride.  Toning  is  the  replace- 
ment of  the  deposited  silver  of  the  print  by  gold  or  platinum,  by 
means  of  a  chloride  solution. 

Gold  occurs  native,  and  alloyed  with  silver  and  other  metals,  and 
combined  with  tellurium. 

It  is  separated  by  alloying  it  with  mercury,  or  by  dissolving  it 
with  cyanides. 

Gold  is  the  most  malleable  metal  and  is  very  ductile. 

Gold  has  a  specific  gravity  of  19.3.  Atomic  weight  197. 
Melting  point  1062°. 

It  is  unaltered  by  air  or  water,  but  dissolves  in  aqua  regia. 
Platinum  occurs  native,  alloyed  with  similar  metals. 

It  is  unattacked  by  air,  water,  and  acids,  except  aqua  regia. 
Caustic  alkalies,  phosphorus,  and  some  other  elements  attack  it 
when  hot. 

Finely  divided  platinum  is  a  powerful  catalytic  agent  for  certain 
purposes. 

A  colloid  is  a  substance  that  forms  uniform,  permanent  sus- 
pensions with  liquids,  and  whose  particles  cannot  pass  through  a 
dialyzing  membrane. 

EXERCISES 

1.  Why  does  not  silver  occur  as  an  oxide  ? 

2.  Give  the  use  of  zinc,  the  cupel,  and  the  electric  current 
in  the  extraction  of  silver. 


EXERCISES  411 

3.  How   much  metallic  silver   can  be  obtained   from   10 
grams  of  silver  nitrate  by  simple  replacement  ? 

4.  Why  is  not  silver  commonly  used  as  an  electric  con- 
ductor ? 

5.  What  is  the  compound  formed  when  silver  tarnishes  ? 

6.  What  gas  much  used  in  the  qualitative  laboratory  would 
discolor  silver  ornaments  worn  there  ? 

7.  What   is   horn    silver?      "Hypo"?    Sterling    silver? 
Lunar  caustic  ?     Oxidized  silver  ? 

8.  In  what  respect  does  coin  silver  differ  from  pure  silver  ? 
How  does  "  Sterling  "  silver  differ  ? 

9.  Compare   the   action  of   silver  with  concentrated  sul- 
phuric acid  and  that  of  zinc  with  dilute  sulphuric  acid. 

10.  Does  coating  glass  with  silver  produce  a  better  mirror 
than  coating  glass  with  tin  amalgam  ?     Discuss. 

11.  What  use  is  mad«  in  the  laboratory  of  the  insolubility 
of  silver  chloride  ?     Write  an  equation  for  its  preparation.    — 

12.  How  much  silver  nitrate  can  be  made  from  a  dime  weigh- 
ing 2.45  grams  ? 

13.  How  could  you  prove  the  presence  of  copper  in  a  silver 
coin? 

14.  Give  the  action  of  the  developer,  the  fixing  bath,  and  the 
toning  solution  in  photography. 

15.  Why  is  it  necessary  to  wash  plates  and  prints  for  a 
long  time  after  fixing  ? 

16.  Gold  is  less  expensive  than  platinum.     Why  is  it  not 
used  in  the  -laboratory  instead  of  platinum  ? 

17.  Give  two  characteristic  properties  and  two  important 
uses  of  (a)  gold ;  (6)  platinum. 

18.  Why  do  gold  and  platinum  occur  chiefly  in  an  uncom- 
bined  condition  ? 


CHAPTER   XXXIV 
ALUMINUM  AND  ITS  COMPOUNDS 

449.  Occurrence.  —  Aluminum   never  occurs   in   a  free 
state,  although  it  is  one  of  the  most  abundant  and  widely 
distributed  elements.     Emery,  corundum,  ruby,  and  sap- 
phire are  more  or  less  pure  forms  of  aluminum  oxide. 
Clay  and  the  rocks  by  the  decomposition  of  which  it  is 
formed  consist  chiefly  of  aluminum   silicate.     Two  min- 
erals of  great  importance  in  the  preparation  of  metallic 
aluminum   are  bauxite,  a  hydrated  oxide   of  aluminum, 
and  cryolite,  a  fluoride  of  sodium  and  aluminum.- 

450.  Preparation.  —  The   only  process  used  at   present 
for  the  extraction  of  aluminum   is  an   electrolytic  one. 
The  electrolyte  consists  of  a  solution  of  aluminum  oxide 
in  melted  cryolite ;  the  cryolite  is  not  decomposed,  but 
serves  as  a  solvent  only.     The  mineral  bauxite  is  used  to 
furnish  the  oxide.     The  cryolite  is  fused  and  kept  liquid 
by  the  heat  generated  during  the  passage  of  the  current ; 
the  dissolved  aluminum  oxide  is  separated  into  aluminum 
and  oxygen  by  the  current.     The  aluminum  collects  as  a 
molten  mass  in  the  bottom  of  the  melting  pot ;  the  oxy- 
gen is  liberated  at  the  anodes,  which  are  oxidized  by  it. 
The  weight  of   the  anodes  consumed  about   equals  the 
weight  of  the  aluminum  liberated. 

The  apparatus  consists  of  a  rectangular  iron  box,  lined 
with  a  thick  layer  of  carbon  which  constitutes  the  cathode 
(Fig.  133).  The  outside  dimensions  are  approximately 

412 


A 


Charles  Martin  Hall  (1863-1914)  was  the  inventor  of  the  elec- 
trolytic process  by  which  aluminum  is  now  produced.  During 
his  course  in  Oberlin  College  he  became  interested  in  aluminum 
and  set  about  to  find  a  cheap  method  of  producing  it.  Failing  in 
his  attempts  to  use  reducing  agents,  he  turned  to  the  electric  current. 
His  problem  was  to  find  a  suitable  solvent  for  aluminum  oxide.  He 
found  that  melted  cryolite  would  serve  this  purpose,  and  after  some 
preliminary  difficulties,  his  process  was  established  on  a  commercial 
basis.  This  process  reduced  the  price  of  aluminum  to  about  eighteen 
cents  per  pound.  It  is  interesting  to  know  that  the  same  process 
was  independently  invented  by  Heroult  in  France.  In  March,  1911, 
Hall  was  awarded  the  Perkin  Medal. 


PHYSICAL  PROPERTIES 


413 


8  feet  long,  4  feet  wide,  and  2  feet  deep.  Carbon  rods 
about  3  inches  in  diameter  and  18  inches  long,  placed  in 
rows,  serve  as  the  anodes.  These  are  so  arranged  that 
they  can  be  lowered  into  the  bath.  The  aluminum  is  al- 
lowed to  run  off  at  the  base  from  time  to  time.  The 
process  is  made  continuous  by  the  addition  of  fresh  sup- 
plies of  aluminum  oxide  as  needed.  The  resistance  of  the 


FIG.  133.  —  ELECTROLYTIC  EXTRACTION  OF  ALUMINUM. 

bath  increases  as  the  oxide  is  decomposed.  The  change  in 
current  operates  a  signal  lamp  which  notifies  the  attendant 
that  the  bath  needs  aluminum  oxide.  Moist  aluminum 
oxide  is  dried  on  a  layer  of  fine  coal  that  floats  on  the  bath. 
The  dry  aluminum  oxide  is  stirred  into  the  bath  from 
time  to  time,  as  it  is  needed. 

451.  Physical  Properties.  —  Aluminum  is  a  silver  white 
metal,  capable  of  a  high  polish.  The  dull  surface  usually 
seen  is  the  result  of  a  thin  coating  of  the  oxide.  Aluminum 
is  lighter  than  any  other  of  the  common  metals,  having 
about  the  same  density  as  glass.  It  is  malleable  and 
ductile,  but  not  very  tenacious.  It  ranks  next  to  silver, 
copper,  and  gold  in  thermal  and  electrical  conductivity. 


414  ALUMINUM  AND  ITS   COMPOUNDS 

452.  Chemical  Properties.  —  Pure  aluminum  is  practically 
unaltered   in   air.     When    aluminum   powder   or   foil   is 
strongly  heated,  it  burns  with  a  very  brilliant  light,  re- 
sembling that  of  magnesium,  and  liberates  a  great  deal 
of  heat. 

Aluminum  is  scarcely  affected  by  nitric  acid  at  any 
temperature.  Dilute  sulphuric  acid  acts  very  slowly 
with  aluminum,  with  the  liberation  of  hydrogen.  With 
the  concentrated  acid  it  behaves  somewhat  like  copper, 
liberating  sulphur  dioxide.  It  reacts  readily  with  hydro- 
chloric acid,  forming  aluminum  chloride.  Aluminum  is 
also  dissolved  by  sodium  and  potassium  hydroxides,  with 
the  formation  of  the  corresponding  aluminates  and  the 
liberation  of  hydrogen: 

2  Al  +  6  KOH  — -*-  2  K8A1O8  +  3  H2 

453.  Uses.  —  Aluminum  has  a  wide  range  of  uses,  al- 
though the  marked  influence  of  a  small  amount  of  impur- 
ities has  made  its  application  more  restricted  than  was 
thought  probable  at  one  time.     Powdered  aluminum  is 
extensively  used  as  a  paint  to  protect  other  metals  from 
corrosion  and  in  flash  powders  for  photography.     Alumi- 
num foil  is  replacing  tin  foil  to  a  considerable  extent. 
Many  small  useful  and  ornamental  articles  are  made  of 
aluminum.     It  is  difficult  to  solder,  so  the  parts  of  the 
larger  articles  are  commonly  welded  together.     Alumi- 
num cooking  utensils,    when   made   of   the   pure   metal, 
prove  very  satisfactory. 

Aluminum  is  being  used  to  a  considerable  extent  in 
place  of  copper  as  an  electric  conductor.  An  aluminum 
wire,  though  larger  than  a  copper  wire  of  the  same  con- 
ducting power,  is  lighter  and  does  not  produce  so  great  a 
strain  on  its  supports.  When  the  price  of  copper  is  high, 


•  THERMIT  PROCESS  415 

aluminum  also  makes  the  cheaper  conductor  of  the  two 
for  carrying  a  given  amount  of  current. 

454.  Aluminum  Alloys.  —  Aluminum  forms   alloys   with 
many  of  the  metals.     The  most  important  is  the  alloy 
with   copper,    called    aluminum  bronze.      This    is   hard, 
elastic,  unaltered  in  air,  easily  cut,  and  has  a  color  closely 
resembling  gold.     It  has  been  successfully  used  in  place 
of  steel  for  small  objects,  such  as  watch  springs  and  ball 
bearings.     Magnalium  is  the  trade  name  for  an  alloy  of 
aluminum  with  magnesium  and  other  metals.     The  metals 
used  with  aluminum  and  their  proportions  vary  according 
to  the  use  to  be  made  of  the  alloy.     It  always  contains 
90  %  aluminum  and  less  than  2  %  magnesium.     The  ten- 
sile strength  of  magnalium  is  much  higher  than  that  of 
aluminum,  and  it  can  be  turned  in  a  lathe.     It  is  less 
corroded  by  air  than  aluminum,  copper,   zinc,  or  brass. 
On  account  of  its  superior  strength  this  alloy  is  replacing 
aluminum  for  many  purposes. 

455.  Thermit  Process.  —  Aluminum  is  a  very  powerful 
reducing  agent.     Owing  to  this  fact,  we  have  a  convenient 
means  of  obtaining  metals  such  as  chromium  and  man- 
ganese in  the  free  state.     When  a  mixture  of  aluminum 
powder  and  an  oxide  of   the  metal  is  ignited,  a  rapid 
combustion  and  a  very  high  temperature  result: 

0203  +  2  Al  — >-  A1203  +  2  Cr 

The  thermit  process,  a  very  valuable  method  for  repairing 
heavy  iron  machinery  and  for  welding  together  the  ends  of 
rails  or  beams,  is  based  on  the  same  principle.  Its  value 
in  this  case  is  chiefly  due  to  the  high  temperature  (3000°) 
produced  in  the  reduction  of  iron  oxide  by  aluminum: 

FeaO3  +  2  Al  — >-  2  Fe  +  A13O3 


416  ALUMINUM  AND  ITS   COMPOUNDS 

This  reduction  takes  place  in  a  conical  shaped  vessel,  from 
which  the  intensely  hot  iron  flows  into  the  crevice  between 
the  two  pieces  of  iron  to  be  joined. 

456.  Aluminum  Oxide.  —  The  occurrence   of   this   com 
pound,  A12O3,  as  corundum  and  emery,  has  already  been 
mentioned.     It  is  easily  formed  as  a  white,  amorphous 
powder  by  igniting  the  hydroxide.     Synthetic  rubies,  sap- 
phires, and  other  gems  can  be  artificially  prepared  by 
fusing  aluminum  oxide  mixed  with  small  quantities  of  com- 
pounds to  give  the  desired  color  ;  potassium  dichromate 
gives  the  ruby  color,  and  a  trace  of  titanium  oxide  pro- 
duces the  sapphire  blue. 

Emery,  aluminum  oxide  mixed  with  various  minerals, 
is  extensively  employed  as  an  abrasive  for  grinding  and 
polishing  on  account  of  its  great  hardness.  An  artificial 
corundum,  made  by  fusing  bauxite  in  an  electric  furnace, 
makes  a  better  abrasive  than  the  natural  emery  and  is 
manufactured  and  sold  under  the  name  of  alundum. 

457.  Double   Salts.  —  If    potassium    sulphate    and    alu- 
minum sulphate  are  mixed  in  water  solution  in  the  pro- 
portion  of    their    molecular    weights,    a    new    substance 
having  a  very  characteristic  crystalline  form  and  all  the 
characteristics  of  a  chemical  compound  is  formed.     This 
is  the  well-known  substance  alum,  KA1(SO4)2  •  12  H2O. 
It  belongs  to  a  class  of  substances  known  as  double  salts. 
Such  salts  contain  two  metals  joined  to  one  kind  of  acid 

radical. 

% 

458.  Alums. — This  class -name  is  given  to  a  series  of 
double  salts  which  have  the   same    crystalline   form   as 
ordinary   alum,  similar   chemical   properties,  and   analo- 
gous formulas.     They  always  contain  a  univalent  metal 
and  a  trivalent  metal.      Chrome   alum   has   the    formula 


PREPARATION  OF  THE  HYDROXIDE  417 

KCr(SO4)2  •  12  H2O  ;  ammonium  alum,  NH4A1(SO4)2 
.  12  H2O.  The  alums  are  much  more  soluble  in  hot  than 
in  cold  water,  and  are  deposited  from  a  cooling  solution 
in  well-marked  crystals,  usually  octahedral  or  cubical  in 
form. 

Ordinary  alum  is  used  for  a  styptic  to  check  the  flow  of 
blood,  and  in  the  preparation  of  aluminum  hydroxide  for 
use  in  mordanting  cloth  and  in  clarifying  water. 


ALUMINUM  HYDROXIDE 

459.  Preparation.  —  This  is  prepared  by  the  addition  of 
ammonium  hydroxide  to  a  solution  of  an  aluminum  com- 
pound. For  example  : 

A12(S04)3  +  6  NH4OH—  ^2  A1(OH)3  +  3  (NH4)2SO4 

Calcium  hydroxide  may  also  be  used.  If  sodium  or 
potassium  hydroxide  is  employed,  it  reacts  in  excess  with 
aluminum  hydroxide,  forming  an  aluminate  and  water  : 


3  KOH  +  A1(OH)3  —  ^K3A1O3  +  3  H2O 

Aluminum  hydroxide  is  an  amorphous,  translucent 
substance,  insoluble  in  water.  It  reacts  with  acids,  form- 
ing the  corresponding  aluminum  salts  ;  but,  as  we  have 
just  seen,  it  also  reacts  with  strong  bases  in  the  manner 
of  an  acid.  Aluminum  hydroxide,  A1(OH)3  or  H3A1O3, 
has,  therefore,  a  double  character,  displaying  one  tend- 
ency or  the  other  according  to  the  nature  of  the  sub- 
stance with  which  it  is  reacting.  This  indicates  ionization 
in  two  different  ways  : 

A1(OH)3  ±5:  Al+++  +  3  (OH)- 
±;  3    H+    +  A10— 


418  ALUMINUM  AND  ITS   COMPOUNDS 

On  heating,  aluminum  hydroxide  is  converted  into 
aluminum  oxide: 

2  A1(OH)3  —v  A1203  +  3  H20 

460.  Mordants  and  Lakes.  —  The    amorphous    character 
of  the  hydroxide  renders  it  valuable  in  dyeing  and  water 
purification.     Many  dyestuffs  do  not  readily  enter  the  fiber 
of  cotton  goods,  so  it  is  necessary  to  use  some  substance  to 
cause  the  dye  to  adhere  and  prevent  it  from  washing  off. 
Such  a  substance  is  called  a  mordant.     It  is  found  that 
when  aluminum  hydroxide  is  precipitated  in  a  solution 
containing  coloring  matter,  the  color  is  carried  down  by 
the  hydroxide  as   it  settles,  leaving  the   solution  clear. 
The  combination  of  the  color  and  aluminum  hydroxide  is 
called  a  lake ;  lakes  are  used  in  dyeing  and  as  pigments. 
In  dyeing  cotton,  aluminum  hydroxide  is  precipitated  on 
the  fiber,  either  by  soaking  the  cloth  first  in  alum  and 
then  in  ammonium  hydroxide  solution,  or  by  impregnat- 
ing it  with  aluminum  acetate,  which  yields  the  hydroxide 
on  heating.     The  cloth,  mordanted  with  aluminum  hy- 
droxide, is  soaked  in  the  dye,  which  forms  an  insoluble 
lake  with  the  mordant,  and  thus  produces  a  fast  color. 
Other  amorphous  hydroxides,  as  those  of  iron  and  copper, 
are  used  as  mordants. 

Many  mordants  react  chemically  with  the  dye,  pro- 
ducing new  shades.  So  it  is  possible,  by  the  use  of  the 
proper  mordants,  to  secure  different  colors  from  the  same 
dye.  This  is  done  in  one  method  of  calico  printing, 
where  the  pattern  is  first  stamped  with  a  mordant.  When 
the  cloth  is  passed  through  the  dye,  the  mordanted  por- 
tions take  it  up  and  retain  it,  while  the  color  is  removed 
from  the  unmordanted  parts  by  washing. 

461.  Coagulum  in  Water  Purification. —The  use  of  alu- 
minum hydroxide  in  water  purification  is  similar  to  that 


COAGULUM  IN   WATER  PURIFICATION         419 


in  dyeing  ;    it  carries  down  with  it  suspended  particles 
of  foreign  matter  (Fig.  134).     The  hydroxide  is  produced 


abed 
FIG.  134.  —  COAGULUM  IN  WATER  PURIFICATION. 

a,  water  containing  fine  particles  in  suspension ;  b,  aluminum  hydroxide 
starting  to  form  throughout  water;  c,  aluminum  hydroxide  settling 
with  the  entangled  suspended  particles ;  d,  purified  water  above 
settlings. 

in  this  case  by  adding  proper  proportions  of  aluminum 
sulphate  and  lime: 

3  Ca(OH)2  +  A12(SO4)3— >-  2  A1(OH)3  +  3  CaSO4 

The  aluminum  hydroxide  is  completely  removed  by  pre- 
cipitation ;  the  precipitate  carries  with  it  the  greater 
part  of  the  sediment  and  disease  germs.  The  calcium  sul- 
phate is  partly  precipitated  and  partly  dissolved,  adding 
to  the  hardness  of  the  water.  In  water  containing  a  con- 
siderable amount  of  calcium,  magnesium,  or  ferrous  bicar- 
bonates  in  solution,  these  salts  are  sufficient  to  precipitate 
the  hydroxide ;  in  such  cases  aluminum  sulphate  or  alum 
is  added  to  the  water  and  the  precipitation  takes  place 
without  lime: 


420  ALUMINUM  AND  ITS   COMPOUNDS 

3  CaHa(C08)a  +  2  Al2(SO4)3  +  6  H2O  — >- 

3  CaS04+3  H2S04+4  Al(OH)3+6  CO2 

3  CaH2(C03)2  +  3  H2SO4-^3  CaSO4  +  6  H2O  +  6  CO2 

ALUMINUM   SILICATES 

462.  Clay  and  Pottery.  —  Ordinary  clay  is  an  impure  silicate 
of  aluminum  ;  kaolin  is  a  pure  form  of  a  similar  deposit. 
Both  are  formed  by  the  decomposition  of  felspar  rock. 
Felspar  is  a  double  silicate  of  aluminum  and  an  alkali 
metal.  When  it  is  exposed  to  the  action  of  the  weather, 
the  alkali  silicate  is  removed  by  the  water  and  carbon 
dioxide,  and  the  residue  left  is  kaolin,  or  clay  containing 
other  rock  materials,  as  sand  and  mica.  Pure  kaolin  is  a 
white,  pulverulent  mass ;  when  wet,  it  is  plastic  and  can 
be  molded.  When  the  molded  clay  is  heated  and  dried, 
it  shrinks.  Iron  compounds  often  give  clay  a  red  color, 
seen  in  some  bricks,  and  in  roofing  and  drain  tiles.  Light 
brick  is  made  from  clay  containing  little  or  no  iron.  Clay 
containing  silica  is  used  for  firebricks,  stove  linings,  and 
crucibles. 

Bricks,  earthenware,  porcelain,  and  china  are  made  by 
molding  the  clay  or  kaolin  into  the  desired  form  and  bak- 
ing in  a  furnace  or  kiln  (Fig.  135).  In  making  common 
earthenware  articles,  the  baking  temperature  is  not  very 
high,  and  the  mass  being  porous,  as  in  flower  pots,  will 
not  hold  water.  In  making  roofing  tiles,  jugs,  and  drain- 
pipes, salt  is  thrown  into  the  fire  ;  it  volatilizes  and  forms 
on  the  surface  of  the  articles  a  glaze  impervious  to  water, 
consisting  of  a  fusible  silicate  of  sodium  and  aluminum. 

Stoneware  and  crockery  are  made  from  purer  varieties 
of  clay,  and  are  more  carefully  molded.  In  addition  to 
the  clay,  they  contain  some  fusible,  hardening  material. 


PORCELAIN  AND   CHINA 


421 


Copyright  by  Underwood  &  Underwood. 

FIG.  135.  —  KILN  BEING  FILLED  WITH  UNBAKED  POTTERY. 

A  heavier  and  more  durable  glaze  is  used  than  that  on 
earthenware. 

463.   Porcelain  and  china  are  made  from   pure  kaolin, 
felspar,    and    quartz.       The    materials   are   ground    finw, 


422 


ALUMINUM  AND  ITS   COMPOUNDS 


Copyright  by  the  Keystone  View  Co. 

FIG.  136.  —  POTTER  AT  WORK. 


thoroughly  mixed,  and  wet.     The  wet  mass  is  then  mod- 
eled.on  a  potter's  wheel  (Fig.  136)  or  molded  in  plaster  of 

Paris  molds  and  dried  ; 
when  dry  enough  to 
handle,  the  mold  is  re- 
moved and  the  article 
smoothed.  It  is  then 
fired  at  a  low  tempera- 
ture which  leaves  it 
firm  and  hard,  but  po- 
rous and  ready  for  the 
glaze.  This  consists  of 
felspar  and  quartz 
ground  fine  and  sus- 
pended in  water.  The 
article  is  dipped  into 
the  mixture  and  dried. 
It  is  then  placed  in  a  Beggar  or  fire-clay  box  (Fig.  137,  5) 
and  supported  on  a  tripod  in  such  a  way  that  it  shall 
not  touch  the  box.  This  is  placed  in  the  kiln,  the  tem- 
perature of  which  is  grad- 
ually raised  to  a  red  heat, 
an  operation  requiring 
from  twelve  to  twenty- 
four  hours.  The  temper- 
ature is  then  increased 
for  three  days  or  more, 
and  finally  allowed  to  fall 
very  slowly.  The  mass  is 
now  hard,  dense,  white, 
translucent,  thin,  and  not 
easily  affected  by  chemi- 
cals, except  alkalies.  The  colors  that  are  used  in  deco- 
rating china  are  composed  of  substances  that  are  stable 


FIG.   137.  —  POTTERY  KILN. 
a,  fire-box ;  b,  seggars. 


SETTING   OF  CEMENT  423 

at  the  high  temperature  necessary  for  the  fusion  of  the 
glaze. 

464.  Cement  and  Concrete.  —  Hydraulic   cement  results 
from  the  heating  of  a  mixture  of  limestone  (calcium  car- 
bonate) and  clay  (aluminum  silicate)  until  they  just  be- 
gin to  melt  together.     Many  natural  limestones  contain 
the  aluminum  silicate  mixed  with  the  calcium  carbonate 
in  nearly  the  required  proportions.     Such  cement  rocks, 
when  burned  in  a  manner  similar  to  that  used  in  making 
quicklime  (§  357),  yield  natural  cements.     Artificial  ce- 
nients  are  made  by  "  burning "  clay  or  shale  with  marl, 
limestone,  or  chalk. 

The  rock  materials  are  crushed  in  the  proportion  of 
about  1  part  of  silicate  to  3  parts  of  carbonate,  and  finely 
powdered.  After  thorough  drying,  the  mixture  is  burned 
in  long,  inclined,  rotary  kilns,  through  which  it  passes 
from  the  comparatively  cool  upper  part  to  the  intensely 
heated  lower  end.  The  lumps  of  the  semi-fused  material 
which  issue  are  cooled  and  ground  to  an  extremely  fine 
powder.  The  quality  of  the  cement  depends  to  an  im- 
portant degree  on  the  fineness  of  the  grinding. 

465.  Setting  of  Cement.  —  Cement  is  believed  to  consist 
of  a  mixture  of  calcium  silicate  and  calcium  aluminate. 
When  it  is  mixed  with  water  and  the  mass  allowed  to 
stand,  it  solidifies  or  "sets."     The   reaction  that  takes 
place  is  probably  a  conversion  of  the  calcium  and  alumi- 
num silicates  of  the  dry  cement  into  other  silicates  of  the 
same   metals  containing   combined  water.     Calcium  hy- 
droxide is  probably  also  set  free  during  this  reaction  and 
hardens  as  it  does  in  the  parts  of  mortar  that  are  not  ex- 
posed to  the  air  (§  362).      As  the  constituents  of  the  air 
have  no  part  in  the  setting  of  cement,  it  goes  on  as  well 


424 


ALUMINUM  AND  ITS   COMPOUNDS 


under  water  as  in  the  air,  and  as  fast  in  the  inside  of  the 
mass  as  on  the  outside.  The  increase  in  hardness  and 
strength  goes  on  rather  rapidly  during  the  first  few  days 
after  the  cement  is  mixed  with  water,  and  then  more 
slowly,  but  the  cement  continues  to  gain  strength  for  years. 


FIG.  138.  —  REENFORCED  CONCRETE  CONSTRUCTION  IN  A  NEW  YORK  SUBWAY. 

466.  Concrete ;  Reenforced  Concrete.  —  The  chief  use  of 
cement  is  in  making  concrete,  a  mixture  of  sand  and 
broken  stone  or  gravel  with  cement  and  water.  Con- 
crete is  used  for  the  foundations,  floors,  and  walls  of 
buildings,  by  pouring  the  wet  concrete  into  forms  made  of 
board  or  steel.  After  it  is  thoroughly  set,  it  gives  a  mass 
that  has  enormous  strength  in  resisting  pressure.  This 
value  may  rise  as  high  as  7000  pounds  to  the  square  inch. 
But  concrete  is  not  so  resistant  against  tensional  (pulling) 
stresses.  To  meet  this  need,  twisted  steel  rods  are  set  in 


SUMMARY  425 

the  molds  in  such  way  a  that  they  become  surrounded  by 
and  enveloped  in  the  concrete  (Fig.  138).  Such  struc- 
tural work  is  known  as  reenforced  concrete.  Its  use  has 
revolutionized  building  processes  in  the  last  few  years. 

Concrete  is  indispensable  for  bridge  piers  and  other 
work  below  water. 

SUMMARY 

Aluminum  does  not  occur  native.  Its  oxides  and  silicates  are 
found  widely  distributed. 

It  is  prepared  by  the  electrolysis  of  oxide  of  aluminum  dissolved 
in  cryolite. 

Aluminum  is  a  silver-white  metal ;  specific  gravity,  2.6 ;  melting- 
point,  657°.  It  is  a  good  conductor  of  electricity. 

Aluminum  dissolves  in  hydrochloric  acid  and  in  potassium 
hydroxide. 

It  is  used  for  making  aluminum  bronze,  cables  for  conducting 
electricity,  paint,  flashlight  powders,  foil,  ornamental  articles,  and 
cooking  utensils. 

Corundum,  ruby,  and  sapphire  are  nearly  pure  aluminum  oxide 
Emery  is  corundum  mixed  with  iron. 

Common  (potash)  alum  has  the  formula  KA1(SO4)2-  12  H20. 
Other  alums  have  the  same  crystalline  form  and  analogous 
formulas.  They  always  contain  a  univalent  metal  and  a  trivalent 
metal  (or  radical). 

Aluminum  hydroxide  possesses  the  properties  of  a  base  and 
those  of  an  acid. 

It  is  used  as  a  mordant  and  in  the  purification  of  water. 

Clay  is  an  impure  silicate  of  aluminum  and  is  used  in  the  manu- 
facture of  bricks  and  of  earthenware. 

Kaolin,  nearly  pure  aluminum  silicate,  is  used  in  the  manufac- 
ture of  porcelain  and  of  china. 


426  ALUMINUM  AND  ITS   COMPOUNDS 

Cement  is  made  by  heating  to  incipient  fusion  a  mixture  of  lime- 
stone and  clay.     Cement  hardens  under  water. 

Concrete  is  a  mixture  of  sand,  broken  stone,  and  gravel  with 
cement  and  water. 

Reenforced  concrete  is  concrete  in  which   steel  rods  are    em- 
bedded to  take  up  the  tensional  stresses. 


EXERCISES 

1.  Would  you  carry  on  .the  electrolysis  of  sodium  chloride 
in  an  aluminum  dish  ?     Would  you  concentrate  a  solution  of 
nitric  acid  in  an  aluminum  vessel  ?     Would  you  concentrate  a 
solution  of  potassium  hydroxide  in  an  aluminum  cup?     Ex- 
plain. 

2.  Name   three   advantages  in   the   use  of  aluminum  for 
kitchen  utensils. 

3.  For  what  purposes  is  aluminum  bronze  used? 

4.  Why  is  aluminum  not  used  for  the   framework  of  bi- 
cycles and  automobiles  ? 

5.  What  would  be  the  weight  of  a  piece  of  aluminum  con- 
taining a  cubic  foot?     A  cubic  foot  of  water  weighs  62.5  Ib. 

6.  How  much  aluminum  is  contained  in  200  tons  of  alumi- 
num oxide? 

7.  Describe  how  the  broken  propeller  shaft   of  an  ocean 
steamer  could  be  repaired  by  thermit.     Show  the  economy  of 
the  process. 

8.  Write  formulas  for  the  following  alums:  sodium  chro- 
mium alum,  ammonium  iron  alum,  potassium  iron  alum. 

9.  How  much  calcium  hydroxide  would  be  required  to  com- 
"bine  with  20  kilos  of  aluminum  sulphate  ? 

10.    Compare  the  action  of  aluminum  sulphate  and  copper 
sulphate  in  water  purification. 


EXERCISES  427 

11.  Write  an  equation  showing  how  aluminum  hydroxide 
can  play  the  part  of  a  base ;  of  an  acid. 

12.  What  compound  of  aluminum  is  formed  when  a  solution 
of  calcium  bicarbonate  reacts  with  a  solution  of  aluminum  sul- 
phate ? 

13.  What  is  a  mordant  ?    A  lake  ? 

14.  What  is  meant  by  saying  that  aluminum  hydroxide  has 
an  amorphous  character  ? 

15.  What  advantage  has  concrete  in  building  foundations 
for  bridge  piers  and  dams? 

16.  Explain  why  steel  rods  are  used  in  reenforced  concrete. 

17.  Compare  the  hardening  of  cement  with  that  of  mortar. 

18.  How  many  liters  of  hydrogen  would  be  liberated  by  the 
addition  of  9  grains  of  aluminum  to  an  excess  of  hydrochloric 
acid? 

19.  Describe   or  define  briefly:    alum,   concrete,   porcelain, 
emery,  aluminum  bronze. 


CHAPTER   XXXV 
TIN  AND  LEAD 

TIN  was  one  of  the  earliest  metals  known.  The  Phoeni- 
cians obtained  it  from  the  British  Isles,  which  they  called 
Cassiterides,  land  of  tin.  As  a  constituent  of  bronze  it 
was  used  before  iron. 

467.  Metallurgy  of  Tin.  —  Tin  oxide,  SnO2,  is  the  only 
available    ore.     The    present    commercial    supply   come's 
principally  from  the  Federated  Malay  States  and  Bolivia. 
Tin  oxide  is  reduced  by  heating  it  in  a  reverberatory 
furnace  with  coal  : 

SnO2  +  C — >-Sn  +  CO2 

The  molten  metal  which  collects  at  the  bottom  of  the 
furnace  is  drawn  off  and  cast  into  ingots,  known  com- 
mercially as  block  tin.  It  is  purified  by  heating  it  on  the 
inclined  hearth  of  a  furnace.  The  less  easily  melted  im- 
purities remain,  while  the  easily  melted  tin  flows  down 
the  hearth.  It  is  further  purified  by  being  poled,  in  the 
same  way  as  blister  copper. 

468.  Properties  of  Tin.  —  Tin  is  a  white,  lustrous  metal, 
capable  of  withstanding  the  ordinary  atmospheric  agents. 
Being  soft  and  malleable,  it  can  be  cut  and  hammered. 
Like  zinc,  it  is  crystalline  in  structure,  and  if  a  bar  of 
tin  is  bent,  it  makes  a  peculiar  noise  (tin  cry),  probably 
caused  by  the   friction   of   the    crystals.     Like   zinc,  its 

428 


TIN 


429 


physical  properties  vary  considerably  with  the  tempera- 
ture. It  melts  at  a  rather  low  temperature,  and  burns, 
forming  a  white  oxide. 

With  acids  tin  does  not  react  like  any  one  of  the  other 
metals  ;  with  hot,  concentrated  hydrochloric  acid,  it  forms 
stannous  chloride,  SnCl2  ;  with  sulphuric  acid  it  reacts  like 


a  b 

FIG.   139.  —  REPLACEMENT  OF  TIN  BY  ZINC. 

a,  five  minutes  after  zmc  has  been  placed  in  stannous  chloride  solution  ; 
b,  twenty  minutes  after. 

copper  ;  nitric  acid  oxidizes  it  to  a  white,  insoluble  solid 
known  as  metastannic  acid. 

Tin  can  be  separated  from  solutions  of  its  compounds 
as  a  gray,  spongy  mass,  by  immersing  a  strip  of  zinc  in 
the  solution  (Fig.  139)  : 


SnCl    +  Zn 


ZnCl2 


469.  Uses  of  Tin.  —  The  resistance  of  tin  to   ordinary 
corrosive  agents  is  utilized  in  protecting  other  metals  by 


430  TIN  AND  LEAD 

covering  them  with  a  layer  of  tin.  Ordinary  tinware  is 
sheet  iron,  which  has  been  thoroughly  cleaned  and  dipped 
into  melted  tin.  Copper  vessels  and  brass  pins  are  sim- 
ilarly treated. 

Tin  foil  is  tin,  hammered  or  rolled  into  thin  sheets  ; 
cheaper  grades  contain  some  lead.  Pipes  made  of  pure 
tin  (block  tin)  are  used  to  convey  soda  water  and  beer  from 
the  tanks  to  the  faucet. 

Many  common  alloys  contain  tin.  Bronze  contains  copper, 
tin,  and  often  zinc.  The  one  cent  piece  is  bronze.  Pew- 
ter and  solder  contain  tin  and  lead.  Britannia  metal  and 
white  metal  contain  varying  proportions  of  tin,  antimony, 
and  copper.  Anti-friction  and  fusible  metals  often  con- 
tain considerable  tin. 

470.  Compounds  of  Tin. — Stannous  chloride,  formed  by 
the  reaction  of  tin  and  hydrochloric  acid,  is  the  only  com- 
mon compound.  The  hydrated  salt,  SnCl2  •  2  H2O  is  tech- 
nically known  as  tin  crystals,  and  is  extensively  used  in 
mordanting.  It*  produces  more  brilliant  shades  than  the 
aluminum  compounds.  Stannous  chloride  is  a  strong 
reducing  agent  in  acid  or  in  alkaline  solutions.  Ferric 
salts  are  reduced  by  it  to  ferrous  compounds : 

2  FeCl8  +  SnCl2  — >-  2  FeCl2  +  SnCl4 

Mercuric  compounds  are  first  reduced  to  mercurous 
salts,  and  with  an  excess  of  the  reagent,  to  metallic  mer- 
cury: 

2  HgCl2  +  SnCl2  — •»-  2  HgCl  +  SnCl4 
2  HgCl  +  SnCl2  — >-  SnCl4  +  2  Hg 

The  stannic  chloride,  SnCl4,  is  a  colorless,  fuming  liquid, 
which  is  readily  decomposed  by  water. 

Thus  the  valence  of  tin  may  be  two  or  four,  as  shown 


METALLURGY  OF  LEAD 


431 


by  the  existence  of  stannous  and  stannic  compounds. 
Stannous  sulphide,  SnS,  is  a  brown,  insoluble  compound. 
Stannic  sulphide,  SnS2,  is  a  yellow,  insoluble  solid  used 
as  a  pigment. 

Cotton  goods  are  rendered  non-flammable  and  stronger 
by  depositing  metastannic  acid  on  the  fibers.  The  goods 
are  dipped  in  a  solution  of  sodium  stannate  (Na2SnO3), 
then  into  a  solution  of  ammonium  sulphate: 


SnCl4  +  6  NaOH 


Na2SnO3  +  4  NaCl  +  3  H2O 
>-  H2SnO3  +  Na2SO4  +  2  NH 


LEAD 

Owing  to  the  wide  distribution  of  its  compounds  and 
the  ease  of  separation  from  its  ores,  lead  has  been  used 
by  man  from  the 

earliest  times. 

471.  Metallurgy. 
—  The  most  com- 
mon ore  is  the  sul- 
phide, galena,  PbS, 
large  deposits  of 
which  are  found  in 
Missouri,  Illinois, 
and  Colorado. 
The  method  em- 
ployed in  the  ex-  FIG.  140.  —  REVERBERATORY  FURNACE. 
traction  depends  largely  upon  the  purity  of  the  ore. 

Ores  having  a  large  percentage  of  lead  are  roasted  in 
a  reverberatory  furnace  (Fig.  140)  until  two  thirds  of  the 
sulphide  has  been  oxidized,  forming  lead  oxide,  sulphur 
dioxide,  and  some  lead  sulphate: 


432  TIN  AND  LEAD 

2  PbS  4-  3  02— ^2  PbO  +  2  S02 
PbS  +  202  — >.PbS04 

When  the  oxidation  has  proceeded  far  enough,  the  air  is 
shut  off  by  closing  the  doors,  and  the  mixture  is  heated 
to  a  higher  temperature.  The  remaining  lead  sulphide 
now  reacts  with  the  lead  oxide  and  sulphate,  forming  lead 
and  sulphur  dioxide: 

PbS  +  2  PbO — ^3  Pb  +  SO2 
PbS  +  PbSO4 — >-  2  Pb  +  2  SO2 

The  lead  is  molded  into  ingots  known  as  pig  lead.  When 
there  is  a  considerable  amount  of  precious  metal  in  the 
lead,  it  is  known  as  base  bullion.  The  working  of  this  has 
been  described  under  silver  (§  426,  Parkes'  process). 

Ores  poor  in  lead  are  reduced  in  a  blast-furnace  similar 
to  that  used  for  copper;  indeed,  they  may  be  separated 
from  the  ore  at  the  same  operation,  the  heavy  lead  set- 
tling beneath  the  matte  and  slag. 

Electrolytic  reduction  of  galena  is  effected  in  a  bath  of 
dilute  sulphuric  acid.  The  crushed  galena  is  made  the 
cathode,  the  bottom  of  the  pan  the  anode.  The  lead  is 
obtained  as  a  spongy  mass.  The  hydrogen  sulphide  pro- 
duced is  conducted  away  to  a  combustion  chamber  and 
converted  into  sulphuric  acid  or  sulphur. 

472.  Properties  of  Lead.  —  Lead  is  a  soft,  bluish  white 
metal.  The  brilliant  luster,  apparent  when  freshly  cut, 
soon  disappears,  owing  to  the  formation  of  a  thin  film  of 
oxide.  This  coating,  however,  protects  it  from  further 
change.  Lead  is  not  very  tenacious,  but  being  soft  it  can 
be  rolled  into  sheets  or  forced  through  a  die  to  form  pipe. 

When  heated  in  air,  lead  oxidizes.  Neither  cold  hydro- 
chloric nor  sulphuric  acid  has  much  effect  on  it.  Nitric 


USES   OF  LEAD 


433 


acid,  acetic  acid  (from  vinegar),  and  many  vegetable  acids 
dissolve  it,  forming  soluble  salts.  Water  containing  car- 
bon dioxide  corrodes  lead,  hence  the 
objection  to  lead  waterpipes,  since  the 
water  by  this  action  might  carry  away 
poisonous  lead  compounds  in  solution. 

All  lead  compounds  are  poisonous, 
and  if  taken  into  the  system  cause 
serious  illness.  Even  minute  quantities 
in  the  water  will  ultimately  produce 
this  result,  for  lead  compounds  are 
excreted  with  difficulty,  and  therefore 
accumulate  in  the  body.  Painter's 
colic  is  a  form  of  chronic  lead  poison- 
ing. 

On  immersing  a  strip  of  zinc  in  a 
solution  of  a  lead  salt,  the  lead  sepa- 
rates in  a  characteristic  crystalline 
deposit,  the  lead-tree  (Fig.  141)  : 

Pb(NO3)2  -h  Zn  — >-  Zn(NO8)2  +  Pb 

The  formation  of  insoluble  chrome  yellow  by  addition  of 
potassium  chromate  to  a  solution  of  a  lead  salt  is  another 
characteristic  property  of  lead  salts : 

Pb(NO3)2  +  K2CrO4  — >-  PbCrO4+  2  KNO3 

473.  Uses  of  Lead.  —  Lead  is  very  extensively  used  for 
pipes  and  as  a  sheathing  for  cables,  as  it  is  easily  cut,  bent, 
or  soldered.  Lead  pipe  is  now  made  by  forcing  the  hot 
lead  through  a  die  by  a  piston.  The  opening  of  the  die 
is  partly  obstructed  by  a  solid  cylindrical  rod  attached  to 
the  upper  surface  of  the  piston.  This  rod  moves  upward 
with  the  piston,  and  the  pipe  is  formed  by  the  lead  being 
squeezed  out  between  the  rod  and  the  wall  of  the  die- 


FIG.  141.  —  REPLACE- 
MENT OF  LEAD  BY 
ZINC. 


434  TIN   AND  LEAD 

Sheet  lead  was  formerly,  used  for  roof  covering  much 
more  than  at  present.  It  is  very  widely  used  as  a  lining 
for  tanks,  cisterns,  and  cells  used  in  electrolytic  opera- 
tions. The  Chinese  have  long  used  it  for  lining  tea 
chests. 

Thin  sheet  lead,  alloyed  with  tin,  is  often  used  instead 
of  pure  tin  foil.  Type  metal  contains  lead,  with  tin  and 
antimony  which  harden  it  and  form  an  alloy  that  ex- 
pands in  solidifying.  Thus  it  fills  the  molds  and  makes 
a  clear-cut  type.  Solder  and  fusible  metals  are  largely 
lead  and  tin.  Such  alloys  are  forced  through  a  die  in  the 
same  manner  as  lead  pipe,  forming  a  wire  used  as  fuse  wire. 

Large  quantities  of  lead  are  used  in  the  manufacture  of 
shot.  As  already  stated,  the  shot  contains  a  small  amount 
of  arsenic.  The  molten  metal  is  run  into  a  perforated 
vessel,  and  falls  in  streams  from  a  considerable  height  into 
the  water.  In  falling,  the  streams  separate  into  drops, 
which  solidify  before  they  reach  the  water.  The  sizes  of 
shot  are  assorted  by  allowing  them  to  run  down  inclined 
planes  and  over  screens  of  different  meshes.  The  small- 
est shot  fall  through  the  nearest  (smallest)  openings  into 
the  bins,  the  larger  shot  going  on  to  the  larger  holes. 
Irregular  shaped  pieces  will  not  roll  well,  and  are  finally 
pushed  off  at  the  end.  The  shot  are  polished  by  tumbling 
them  in  a  barrel  or  drum  with  a  little  graphite. 

COMPOUNDS   OF  LEAD 

474.  Oxides. — Lead  oxide,  PbO,  when  of  a  yellowish  tint, 
is  known  as  massicot ;  when  it  solidifies  from  the  molten 
state  it  is  buff-colored  and  crystalline,  and  is  known  as 
litharge.  The  presence  of  bismuth  sometimes  gives  the 
litharge  a  yellowish  color.  Litharge  is  made  by  heating 
lead  in  the  air.  Considerable  quantities  are  produced  in 


WHITE   LEAD  435 

the  cupellation  of  silver.  It  is  largely  used  in  the  prepa- 
ration of  oils  and  varnishes,  of  glass  and  glazes,  and  of 
other  compounds  of  lead.  A  mixture  of  litharge  and 
glycerine  is  used  as  a  cement,  especially  for  stone  and 
glass. 

Red  lead,  or  minium,  is  a  bright  red  powder,  known  as 
American  vermilion.  It  is  prepared  by  heating  lead  or 
lead  oxide  in  the  air,  oxygen  being  absorbed  in  the  opera- 
tion. The  tint  and  composition  often  vary  with  the  ma- 
nipulation. Its  composition  may  be  represented  by  the 
formula :  Pb3O4  or  (2  PbO  •  PbO2).  It  is  used  in  making 
flint  glass  and  as  a  pigment,  especially  on  ironwork.  Be- 
ing an  oxidizing  agent,  it  hastens  the  hardening  of  the  oils 
used  in  paint.  On  this  account  a  mixture  of  red  lead  and 
oil  is  used  by  plumbers  and  gas  fitters  to  make  tight  joints. 

Lead  dioxide,  PbO2,  also  called  lead  peroxide,  is  a  brown 
powder  obtained  by  treating  red  lead  with  nitric  acid. 
It  is  used  as  an  oxidizing  agent  on  the  positive  plates  of 
storage  batteries. 

475.  White  Lead,  or  basic  lead  carbonate,  is  a  heavy, 
white,  opaque  powder.  It  mixes  well  with  linseed  oil 
and  forms  a  valuable  paint  base.  The  body  of  many 
paints  is  white  lead,  which  furnishes  opacity  or  body,  dif- 
ferent colors  being  produced  by  the  addition  of  colored 
pigments.  Owing  to  the  importance  of  white  lead,  many 
methods  have  been  devised  for  its  production. 

The  Dutch  process  of  corrosion  has  been  in  use  three 
hundred  years,  and  although  details  have  been  improved, 
remains  essentially  the  same.  Ridged  and  perforated 
disks,  or  "buckles,"  of  lead  (Fig.  142)  are  piled  in  a 
loosely  covered  earthenware  pot,  the  lower  part  of  which 
contains  a  little  dilute  acetic  acid.  Such  pots  are  placed 
side  by  side  and  covered  with  moist  tan  bark;  other  layers 


436 


TIN  AND  LEAD 


of  pots  are  added  to  a  considerable  height.  The  decay- 
ing organic  matter  generates  heat  and  carbon  dioxide. 
The  acetic  acid  is  volatilized,  forming  basic  lead  acetate. 
The  carbon  dioxide  resulting  from  the  fermentation 
changes  this  to  the  basic  carbonate.  Three  or  four  months 
are  required  for  the  complete  corrosion  of  the  lead;  the 
right-hand  portion  of  Fig.  142  represents  a  jar  broken 
open  to  show  the  lead  buckles  after  corrosion.  The  white 
lead  is  removed  from  the  jars,  and  small  pieces  of  un- 

altered lead  are  removed 
by  screening.  It  is  then 
ground  wet,  washed, 
strained  through  fine  silk 
sieves,  and  allowed  to  set- 
tle. The  white  lead  is 
finally  ground  in  oil  and 
is  ready  for  use.  The  cor- 
rosion process  requires 

much  time  but  yields  good  paint.  The  Dutch  process  aims 
at  a  white  lead  with  the  composition  Pb(OH)3  .  2  PbCO3, 
but  the  composition  of  the  product  varies. 

A  much  quicker  corrosion  is  obtained  by  blowing  the 
melted  lead  into  a  fine  spray  by  a  blast  of  steam,  and  treat- 
ing the  resulting  powder  with  a  stream  of  carbon  dioxide 
in  the  presence  of  moist  air  and  acid,  in  a  rotating  cylinder. 
The  commercial  white  paints  are  generally  mixtures  of 
white  lead  and  zinc  white.  Calcium  carbonate,  barium  sul- 
phate, silica,  and  other  substances  are  frequently  used  as 
extenders. 


476.   Chrome  Yellow.—  Zead  chr  ornate,  PbCrO4,  is  an  in- 

soluble, bright  yellow  powder,  prepared  by  mixing  solu- 
tions of  lead  salts  and  chromates.  It  is  used  in  dyeing 
and  painting. 


EXERCISES  437 


SUMMARY 

The  chief  ore  of  tin  is  the  oxide,  which  is  reduced  by  heating 
with  coal. 

Tin  is  soft,  malleable,  and  crystalline.  Its  specific  gravity  is 
7.3,  and  it  melts  at  232°  C. 

It  is  unaltered  by  air  at  ordinary  temperatures. 

Tin  is  used  for  pipe,  as  foil,  and  as  a  coating  for  iron.  It  is  a 
constituent  of  bronze,  pewter,  and  white  metal. 

Stannous  chloride  is  formed  by  the  action  of  hydrochloric  acid 
on  tin.  It  is  a  reducing  agent. 

Lead  occurs  chiefly  as  a  sulphide.  .  The  ore  is  reduced  in  a 
reverberatory  furnace,  or  by  electrolysis. 

Lead  is  soft,  malleable,  and  tenacious.  Its  specific  gravity  is 
about  1 1.3  and  its  melting  point  327°  C. 

It  oxidizes  in  air  and  dissolves  in  nitric  and  acetic  acids.  Water 
containing  carbon  dioxide  corrodes  it,  producing  poisonous  com- 
pounds. 

Lead  is  used  for  pipe,  as  a  lining,  a  covering  material,  and 
in  alloys,  such  as  type  metal,  solder,  and  shot. 

Lead  oxides  are  made  by  heating  lead  in  air.  They  are  used  in 
making  varnishes  and  glass,  and  as  pigments.  Lead  dioxide  is 
used  in  storage  batteries. 

White  lead  is  basic  lead  carbonate.  Chrome  yellow  is  lead 
chromate. 

EXERCISES 

1.  Which  forms  the  better  protective  coating  for   iron, — 
tin  or  zinc  ? 

2.  State  the  relative  advantages  of  lead  and  tin  plate  as  a 
coating  for  roofs. 


438  TIN  AND  LEAD 

3.  Why  were  lead  and  tin  early  obtained  in  the  metallic 
state  ? 

4.  Why  is  tin  foil  superior  to  lead  foil  for  wrapping  articles 
of  food? 

5.  Why  is  arsenic  put  in  shot  ? 

6.  What  is  litharge  ?     Red  lead  ?     White  lead  ? 

7.  Why  is 'red  lead  called  a  drier  in  paints  and  varnishes  ? 

8.  What  advantage  has  zinc  white  over  white  lead   as   a 
paint  base  ?     White  lead  over  zinc  white  ? 

9.  What  are  the  characteristic  properties  of  glass  contain- 
ing lead  ? 

10.  How  much  lead  can  be  extracted  from  a  ton  of  galena  ? 

11.  In  converting  a  ton  of  lead  oxide  (PbO)  into  red  lead 

,  how  much  oxygen  is  absorbed  ? 


CHAPTER   XXXVI 

MANGANESE,  CHROMIUM,  COBALT,  AND  NICKEL 
MANGANESE 

477.  Preparation  and  Properties.  —  The  most  important 
ore  of  manganese  is  pyrolusite,  which  is  crude  manganese 
dioxide.     The  metal  is  obtained  by  igniting  a  mixture  of 
pyrolusite  and  aluminum  powder.     Heat  is  applied  at  one 
point  and  the  action  spreads  through  the  whole  mass : 

3  MnO2  4-  4  Al  — >-  2  A12O3  +  3  Mn 

Manganese  is  a  hard  metal  resembling  steel  in  appear- 
ance. It  oxidizes  in  moist  air  and,  when  finely  divided, 
decomposes  boiling  water.  It  dissolves  readily  in  sul1 
phuric  and  hydrochloric  acids,  with  the  liberation  of  hy- 
drogen and  the  formation  of  the  corresponding  salt  of  the 
manganous  ion,  Mn++  : 

Mn  +  H2S04  — ^  MnS04  +  H2 

Its  alloys  with  iron,  ferro-manganese,  and  spiegeleisen  are 
used  in  the  production  of  Bessemer  iron  and  steel. 

478.  Manganese  Compounds.  —  Manganese  forms  several 
oxides,  of  which  the  most  important  is  the  dioxide,  MnO2. 
This  is  a  hard,  black  solid  which  conducts  electricity.     It 
is  a  powerful  oxidizing  agent,  as  we  have  already  seen  in 
the  preparation  of  chlorine  from  hydrochloric  acid  (§  75). 
Its  conducting  power  and  oxidizing  action  make  it  a  valu- 
able depolarizer  in  voltaic  cells. 

439 


440    MANGANESE,  CHROMIUM,  COBALT,  AND  NICKEL 

The  manganous  salts  are  stable  compounds,  whose 
water  solutions  are  pink.  The  salts  of  the  manganic  ion 
Mn++++  are  unstable. 

479.  Manganates  and  Permanganates.  —  Since  manganese 
is  one  of  the  elements  that  display  both  metallic  and  non- 
metallic  characteristics,  we  have  salts  in  which  it  occurs 
as  a  constituent  of  the  negative  ion. 

The  most  important  of  these  salts  are  the  manganates 
and  the  permanganates,  both  of  which  contain  the  radical 
MnO4.  In  the  manganates  the  ion  is  bivalent,  MnO4 ; 
in  the  permanganates  it  carries  only  one  charge,  MnO4~. 
Corresponding  to  this  difference  in  valence  of  the  ion  are 
differences  in  the  properties  of  the  salts.  The  manga- 
nates are  green  and  the  permanganates  are  purple. 

Potassium  manganate  is  made  by  fusing  a  manganese 
compound  with  potassium  hydroxide  in  the  presence  of 
air  or  an  oxidizing  agent,  dissolving  the  residue  and 
evaporating  the  solution  in  a  vacuum.  The  crystals  ob- 
tained are  dark  green.  They  are  decomposed  by  water, 
with  the  liberation  of  manganese  dioxide  and  the  forma- 
tion of  potassium  permanganate,  KMnO4: 

3  K2Mn04  +  2  H2O  — >-  2  KMnO4  +  MnOa  +  4  KOH 

Potassium  permanganate  is  obtained  as  dark  purple 
crystals,  which  dissolve  in  watjer,  yielding  a  violet  solution. 
It  is  a  powerful  oxidizing  agent. 

CHROMIUM 

jtr  TT 

480.  Chromium  occurs  chiefly  as  chromite,"  Cr203  •  FeO. 
From  this  it  is  reduced  by  aluminum  in  a  manner  analo- 
gous to  that  employed  in  the  preparation  of  manganese. 
It  is   a   hard,   steel-gray   metal,    unaltered    by   the   air. 


CHROMATES  AND  BICHROMATES  441 

When  very  small  quantities  are  added  to  steel,  the  tenacity 
and  hardness  are  increased. 

481.  Oxides  of  Chromium.  —  The  two  important  oxides 
of  chromium  are  chromic  oxide,  Cr2O3,  and  chromic  anhy- 
dride, CrOg.     The  chromic  salts  are  derived  from  chromic 
oxide ;  the  most  important  is  the  double  sulphate  of  po- 
tassium and   chromium,  KCr(SO4)2  •  12  H2O,  known  as 
chrome  alum.     A   solution  of  chromic  anhydride   yields 
CrO4       ions,  but  the  acid  is  isolated  with  difficulty,  as  it 
breaks  up  into  chromic  anhydride  and  water.     The  solu- 
tion of  the  anhydride  is  a  powerful  oxidizing  agent,  and 
its  derivatives,  the  chromates  and  dichromates,  resemble 
it  in  this  respect. 

482.  Chromates  and  Bichromates.  —  Potassium  dichromate, 
K2Cr2O7,  is  the  source  of  most  of  the  chromium  salts.     It 
is  prepared  by  heating  chromite  with  potassium  carbonate 
and  lime  in  a  reverberatory  furnace.     It  forms  large  red 
crystals  from  solution  or  fusion ;  these  are  somewhat  sol- 
uble in  cold  water,  and  their  solubility  increases  rapidly 
as  the  temperature  rises.     Potassium  dichromate  reacts 
with  sulphuric  acid  in  the  presence  of  an  oxidizable  sub- 
stance, with  the  formation  of  chromium  sulphate  and  the 
liberation  of  oxygen.     This  oxidizing  action  is  frequently 
made  use    of  in  depolarizing  voltaic  cells.      Sodium  di- 
chromate is  very  similar  to  potassium  dichromate,  but  has 
the  added  advantage  of  being  more  soluble.     Most  of  the 
dichromates  are  orange  in  solution. 

Potassium  chromate,  K2CrO4,  is  prepared  by  the  addi- 
tion of  potassium  hydroxide  to  the  dichromate  : 

K2Cr2O7  +  2  KOH  -^-  2  K2CrO4  +  H2O 

It  forms  yellow  crystals,  more .  soluble  than  those  of  the 
dichromate. 


442    MANGANESE,  CHROMIUM,  COBALT,  AND  NICKEL 

The  acids  from  which  the  chromate  and  the  dichromate 
are  theoretically  derived  have  the  formulas  H2CrO4  and 
H2Cr2O7  respectively.  Both  of  these  have  the  anhydride 
CrOg,  as  may  be  seen  from  the  theoretical  equations : 

HaO  +  Cr08— ^H2Cr04 
H20  +  2  Cr03  — >-  H2Cr207 

The  relation  between  the  chromate  and  the  dichromate  is 
shown  if  the  formula  of  potassium  dichromate  is  written 
K2CrO4  •  CrO3.  Other  complex  chromates  are  known 
containing  more  than  one  CrO3  group. 

Lead  chromate,  PbCrO4,  made  by  treating  a  soluble  lead 
salt  with  a  chromate  or  dichromate,  is  a  yellow,  insoluble 
compound,  known  as  chrome  yellow,  and  used  as  a  pig- 
ment. The  chromates  of  zinc  and  barium  are  also  used  as 
pigments. 

483.  Change  of  Valence  through  Oxidation.  --In  cases  of 
elements  which  have,  like  manganese  and  chromium,  a 
wide  variety  of  compounds,  the  change  of  the  element 
from  one  compound  into  another  is  frequently  accom- 
panied by  a  change  of  valence.  We  will  consider  the 
case  of  chromium  briefly. 

Chromous  chloride,  CrCl2,  in  which  the  valence  of  the 
metal  is  2,  can  be  changed  into  chromic  chloride,  CrCl3, 
where  the  valence  is  3,  by  an  oxidizing  agent.  The  pres- 
ence of  hydrochloric  acid  enables  us  to  write  a  simpler 
equation  : 

2  CrCl2  +  2  HC1  +  O  — >-  2  CrCl3  +  H2O 

Chromic  compounds  can  be  converted  into  chromates  by 
melting  them  with  a  base  and  an  oxidizing  agent,  such  as 
potassium  chlorate : 

2  CrCl,  +  10  KOH  +  3  O  — >•  2  K2CrO4  +  6  KC1  +  5  H2O 


OCCURRENCE  OF  NICKEL  443 

The  valence  of  chromium  in  potassium  chromate  is  shown 
to  be  6  by  the  following  diagram  of  the  arrangement  of 
the  atoms  : 

K-°\c/° 

K— O/     V) 

Hence  it  appears  that  in  the  reaction  given,  chromium  has 
again  undergone  a  change  in  valence  brought  about  by 
an  oxidizing  agent. 

Reducing  agents  produce  reverse  changes. 

These  facts  represent  a  general  principle  which  may  be 
stated  thus  :  Oxidizing  agents  tend  to  produce  actions  in 
which  valence  is  raised;  reducing  agents  tend  to  produce 
actions  in  which  valence  is  lowered. 

The  change  of  chromates  into  dichromates,  and  the  re- 
verse changes,  do  not  involve  changes  of  valence,  since 
both  salts  are  derived  from  the  same  anhydride. 

NICKEL 

484.  Occurrence.  —  The  greater  part  of  the  nickel  that 
the  world  uses  comes  from  the  province  of   Ontario  in 
Canada,    and    from   New   Caledonia.     The   nickel   com- 
pounds in  the  ores  form  only  a  small  part  of  the  whole. 
The  Canadian  ore  is  chiefly  a  sulphide  of  iron,  containing 
about  2%  each  of  nickel  and  copper.     Nickel  is  nearly 
always  a  constituent  of  meteoric  iron. 

485.  Extraction.  —  The   sources  of  nickel  are  complex 
minerals,  chiefly  sulphides  and  arsenides  mixed  with  large 
quantities  of  other  materials.     The  separation  of  nickel 
from   such   mixtures  presents  a  complex  problem.     The 
low  percentage  of  nickel  contained  in  the  ore  makes  it 
necessary  to  produce,  by  methods  of  concentration,  a  sub- 


444    MANGANESE,  CHROMIUM,  COBALT,  AND  NICKEL 

stance  containing  a  higher  percentage  of  nickel  before 
processes  for  smelting  are  carried  on.  To  accomplish 
this,  use  is  frequently  made  of  the  fact  that  nickel  has  a 
greater  affinity  for  arsenic  than  any  of  the  metals  with 
which  it  is  found  associated,  and  of  the  fact  that  nickel 
stands  next  to  copper  in  its  affinity  for  sulphur. 

If  the  ore  contains  no  copper,  or  -in  case  the  copper  is  to 
remain  alloyed  with  the  nickel,  it  is  usual  to  make  either 
(a)  nickel  matte,  or  (5)  nickel  speiss. 

Nickel  matte  is  made  when  the  ore  consists  of  sulphides. 
The  process  is  similar  to  that  described  (§  415)  for  the 
production  of  copper  matte.  Nickel  matte  contains  about 
40  %  of  nickel,  and  is  a  mixture  of  sulphides. 

Nickel  speiss  is  made  when  the  ore  is  a  mixture  of 
arsenides ;  it  is  itself  a  complex  arsenide  of  nickel,  iron, 
and  frequently  of  other  metals.  The  process  of  making 
it  resembles  that  used  for  the  production  of  matte,  and  it 
contains  from  40  %  to  50  %  nickel.  In  case  copper  is  to  be 
eliminated,  one  of  the  simpler  methods  takes  advantage  of 
the  affinity  of  copper  for  sulphur  and  of  nickel  for  arsenic. 
The  compounds  formed  are  but  slightly  soluble  in  each  other. 

The  nickel  matte  (or  the  nickel  speiss)  is  then  con- 
verted into  nickel  oxide  by  oxidation  in  a  reverberatory 
furnace  or  a  converter.  The  production  of  arsenic  oxide, 
a  substance  which  is  highly  poisonous  and  which  is  in- 
jurious to  vegetation,  is  avoided  by  using  a  mixture  of 
sodium  carbonate  and  sodium  nitrate  to  convert  the  arsenic 
into  sodium  arsenate,  which  is  readily  removed  by  dis- 
solving in  water. 

The  nickel  oxide  is  reduced  by  mixing  it  with  flour 
paste,  rolling  and  cutting  the  mixture  into  small  cubes, 
which  are  dried,  embedded  in  charcoal,  and  heated.  The 
nickel  cubes  thus  obtained  are  suitable  for  making  alloys, 
but  are  too  impure  for  nickel  ware. 


USES   OF  NICKEL  445 

The  Mond  method  is  used  for  the  production  of  pure 
nickel  from  the  ore.  This  method  is  based  on  the  fact 
that  nickel  will  combine  directly  with  carbon  monoxide  to 
form  nickel  carbonyl,  Ni(CO)4.  Nickel  oxide,  produced 
in  smelting  the  ore,  is  reduced  to  nickel  in  a  porous  form 
by  heating  in  the  presence  of  hydrogen.  Carbon  mon- 
oxide at  a  temperature  of  100°  C.  and  a  pressure  of  15 
atmospheres  is  then  passed  over  the  porous  nickel  to  con- 
vert it  into  nickel  carbonyl.  The  vapors  of  nickel  car- 
bonyl are  decomposed  by  heating  them  to  200°  C.  under 
atmospheric  pressure.  The  carbon  monoxide  is  recovered 
for  the  conversion  of  a  new  lot  of  nickel  into  nickel  car- 
bonyl. The  direction  in  which  the  reversible  equation 


runs  depends  upon  temperature  and  pressure. 

486.  Properties  of  Nickel.  —  Nickel  is  a  hard  metal,  mal- 
leable, possessing  a  high  melting  point,  and  resembling 
silver  in  color.     It  is  capable  of  receiving  and  retaining 
a  very  high  polish.     Dry  air  does  not  attack  it.     Like 
cobalt,  it  dissolves  readily  in  nitric  acid,  but  is  only  slowly 
attacked  by  hydrochloric  and   sulphuric  acids.     Nickel- 
plated  ware  should  never  be  scoured,  but  should  be  cleaned 
by  washing  with  soap  suds  and  burnishing  with  a  cloth. 

Solutions  of  nickel  salts  have  a  beautiful,  characteristic 
green  color.  Nickel  and  cobalt  resemble  iron  in  being 
attracted  by  a  magnet.  Their  chemical  properties  are  also 
similar  to  those  of  iron. 

487.  Uses.  —  Nickel  is  of  considerable  practical  impor- 
tance because  of  its  silver-  white  color  and  the  fact  that  it 
does  not  readily  tarnish  in  air.    It  is  chiefly  used  as  a  cover- 
ing for  other  metals.     It  is  deposited  by  an  electrolytic 


446    MANGANESE,  CHROMIUM,  COBALT,  AND  NICKEL 

process  similar  to  that  used  in  silver  or  copper  plating. 
Nickel  is  a  constituent  of  several  important  alloys.  Nickel 
steel,  which  contains  about  5%  nickel,  is  both  hard  and 
tough;  it  is  used  in  making  armor  plates  for  battle  ships. 
Nickel  coins  contain  about  one  part  nickel  to  three  parts 
copper. 

488.  Compounds.  —  The  sulphate,  NiSO4,  and  a  double 
sulphate  of  nickel  and  ammonium  are  the  salts  used  as 
electrolytes  in  nickel  plating. 

COBALT 

As  no  industrial  use  is  made  of  pure  cobalt,  the  metal  is 
seldom  extracted. 

489.  Cobalt  Ores. — Cobalt  is  found  as  a  minor  constituent 
of  ores  of  complex  composition.     These  ores  are  usually 
sulphides  or  arsenides,  in  which  iron  is  the  predominating 
metal,  though  they  contain   copper  and   nickel   as  well. 
Cobalt  speiss,  CoAs2,  is  found  in  Saxony;  cobalt  glance, 
CoAs2  •  CoS2,  in  Norway  and  Sweden.     The  ores  are  usu- 
ally worked  up  to  obtain  cobalt  compounds  without  sepa- 
rating the  element  in  the  metallic  state.     They  are  first 
roasted  to  remove  sulphur  and  arsenic,  and  the  resulting 
oxides  are  then  dissolved  in  acids. 

490.  Properties  of  Cobalt.  —  Cobalt  is  a  hard,  magnetic 
metal,  malleable  and  ductile,  and  capable  of  receiving  a 
high  polish.     Its  melting  point,  like  that  of  iron,  is  high. 
It  dissolves  readily  in  nitric  acid,  but  is  acted  on  slowly 
by  other  acids.    Solutions  of  cobalt  salts  have  a  rose  color. 

491.  Cobalt  Compounds.  —  The  chloride,  CoCl2,  and  the 
nitrate,  Co(NO3)2,  are  of  some  importance.     The  chloride 
has  a  peculiar  property  of  changing  its  color  when  ex- 


COBALT  COMPOUNDS  447 

posed  to  air  of  varying  humidity.  These  changes  are  ex- 
plained by  the  fact  that  the  substance  forms  a  number  of 
different  compounds  with  varying  amounts  of  water  of 
crystallization  and  passing  readily  into  one  another.  The 
less  hydrated  forms  are  blue  or  lavender,  while  the  more 
hydrated  are  red.  Heated  or  exposed  to  dry  air,  the  red 
salt  loses  water  of  crystallization,  and  is  changed  to  a  blue, 
less  hydrated  form.  Advantage  is  taken  of  this  fact  to 
make  "  s}^mpathetic  ink,"  which  is  invisible  until  heated, 
and  for  simple  apparatus  to  indicate  the  amount  of  mois- 
ture in  the  air. 

Cobalt  nitrate,  Co(NO3)2,  is  sometimes  used  in  analytical 
work  in  testing  for  certain  metals.  It  unites  with  certain 
metallic  oxides,  forming  characteristically  colored  com- 
pounds. Thus  aluminum  compounds,  when  converted 
into  the  oxide  by  heating  with  the  blowpipe,  give  a  blue 
coloration  when  further  heated  with  cobalt  nitrate 
solution. 

Cobalt  sulphide,  CoS,  black  in  color,  is  precipitated  from 
alkaline  solutions  of  cobalt  salts  by  hydrogen  sulphide. 
Like  iron,  cobalt  forms  two  double  cyanides  with  potas- 
sium, K4Co(CN)6  and  K3Co(CN)6. 

SUMMARY 
Manganese 

Manganese  occurs  chiefly  as  pyrolusite,  crude  manganese 
dioxide. 

Manganese  alloys,  ferro-manganese  and  spiegeleisen,  are  much 
used  in  the  steel  industry.  Several  forms  of  iron  and  steel  con- 
tain manganese. 

Manganese  dioxide,  MnO2,  insoluble,  and  potassium  perman- 
ganate, soluble,  are  two  important  oxidizing  agents. 


448    MANGANESE,  CHROMIUM,  COBALT,  AND  NICKEL 

Chromium 

Chromium  occurs  less  abundantly  than  manganese,  chiefly  as 
chromite,  Cr203  •  FeO. 

Chromium  is  used  in  making  chrome  steel,  a  very  hard  and 
tenacious  alloy. 

Important  chromium  compounds  are:  chromic  oxide,  Cr2O3, 
used  as  a  green  pigment;  chrome  alum,  KCr(S04)2-  12  H20, 
used  in  tanning;  lead  chromate,  PbCr04,  used  as  a  yellow 
pigment ;  potassium  chromate,  K2Cr04,  and  potassium  dichromate, 
K2Cr2O7,  used  as  oxidizing  agents. 

A  wide  variety  of  compounds  are  formed  by  both  manganese 
and  chromium.  This  is  due  to  two  facts  :  (a)  both  elements  dis- 
play both  metallic  and  non-metallic  characteristics  ;  (b)  both  ele- 
ments display  several  different  valences. 

In  causing  elements  to  change  through  a  series  of  compounds 
oxidizing  and  reducing  agents  play  an  important  part.  Oxidizing 
agents  tend  to  raise  valence,  reducing  agents  to  lower  it. 

Nickel 

When  a  nickel  ore  contains  arsenic,  nickel  will  take  arsenic 
from  the  other  metals  until  it  is  satisfied.  During  the  process  a 
portion  of  the  other  metals  will  be  oxidized  and  the  oxides  will 
pass  into  slag.  When  copper  is  not  present  a  similar  statement 
is  true  concerning  the  behavior  of  nickel  towards  sulphur. 

A  substance  rich  in  nickel  arsenide  is  known  as  nickel  speiss. 
Nickel  matte  is  a  substance  rich  in  nickel  sulphide. 

Nickel  oxide  is  obtained  from  nickel  speiss  or  from  nickel  matte 
by  oxidation  in  a  furnace. 

Cubes  of  somewhat  impure  nickel  are  formed  by  reducing 
nickel  oxide  by  mixing  it  with  flour  and  heating  in  charcoal. 

Pure  nickel  is  obtained  by  making  use  of  the  facts  that  carbon 
monoxide  under  pressure  and  at  a  temperature  of  100°  C.  con- 


EXERCISES  449 

verts  nickel  into  nickel  -carbonyl  (Ni(CO)4)  and  that  the  vapor  ot 
nickel  carbonyl  decomposes  at  200°  C. 

Nickel  does  not  tarnish  in  dry  air  and  is  used  for  making  alloys 
and  as  a  protective  coating  for  iron. 

Cobalt 
Metallic  cobalt  is  rarely  extracted. 

Important    cobalt  compounds    are    the    chloride,   nitrate,    and 
sulphide. 

EXERCISES 

1.    How  is   manganese  obtained   in  the   free   state   from 
pyrolusite  ? 

2. .  Why  is  spiegeleisen  used  in  making  Bessemer  steel  ? 

3.  Why  is  manganese  dioxide  mixed  with  carbon  in  a  dry 
cell? 

4.  Which  is  the  easier  to  preserve,  potassium  manganate  or 
potassium  permanganate  ?     Why  ? 

5.  What  qualities  does  chromium  give  to  steel  ?     For  what 
purposes  is  chrome  steel  suited  ? 

6.  Explain  the  relation  between  potassium  chromate  and 
potassium  dichromate. 

7.  Why  is  the  change  of  chromous  into  .chromic  chloride 
spoken  of  as  oxidation  ? 

8.  During  the  smelting  of  nickel  ores,  what  is  the  object  in 
producing  nickel  speiss  or  nickel  matte  ? 

9.  How  is  nickel  speiss  converted  into  nickel  oxide  ? 

10.  How  would  nickel  oxide  be  treated  if  the  nickel  were  to 
be  used  for  making  alloys  ?     For  making  nickel  ware  ? 

11.  Why  is  iron  often  plated  with  nickel  ? 

12.  Name  an  acid  in  which  nickel  dissolves  readily. 

13.  Name  three  metals  that  are  attracted  by  a  magnet. 

14.  Explain  the  action  of  sympathetic  ink. 


CHAPTER   XXXVII 
THE  PERIODIC  LAW 

492.  Early  Attempts  at  Classification.  —  The  discovery  of 
new  elements  and  the  investigation  of  their  properties  led 
the  earlier  chemists  to  recognize  the  existence  of  certain 
families  or  groups  of  elements.  In  1829  Dobereiner 
called  attention  to  certain  triads  or  groups  of  three  ele- 
ments in  which  the  atomic  weight  of  the  second  element 
was  the  arithmetical  mean  of  the  first  and  third.  He 
also  pointed  out  that  the  properties  of  the  middle  element 
were  intermediate  between  those  of  the  other  two.  This 
was  the  first  attempt  to  show  that  a  relation  existed  be- 
tween the  properties  of  elements  and  their  atomic  weights. 
The  elements  chlorine,  bromine,  and  iodine  form  a  well- 
marked  triad  : 

35.5  +  127  o. 


the  atomic  weight  of  bromine,  80,  approximates  the  mean, 
81.2. 

Other  attempts  to  classify  the  elements  were  made  from 
time  to  time,  but  it  was  not  until  1860-1870  that  any  sys- 
tem received  recognition.  In  1863-1864  Newlands,  an 
Englishman,  directed  attention  to  the  fact  that  the  ele- 
ments showed  surprising  regularity  when  arranged  in 
order  of  their  atomic  weight.  He  said  the  properties  of 
each  element  seemed  to  be  repeated  in  a  measure  by  those 
of  the  eighth  element  following  it.  This  relation  is  called 

450 


2£*u^ 

Dimitri  Ivanovitch  Mendelejeff  (1834-1907)  was  born  in 
Tobolsk,  Siberia.  Through  the  efforts  of  his  mother,  who  estab- 
lished a  glass  works,  he  received  an  excellent  education  in  Tobolsk 
and  St.  Petersburg.  He  spent  the  greater  portion  of  his  life  as 
Professor  of  Chemistry  in  the  University  of  St.  Petersburg,  and 
to  him  Russia  owes  the  training  of  two  generations  of  chemists, 
as  well  as  the  development  of  its  petroleum  and  other  chemical 
industries.  Although  there  was  no  section  of  the  chemical  science 
of  his  time  which  was  not  enriched  by  his  contributions,  the  fame 
of  Mendelejeff  rests  secure  on  the  setting  forth  and  establishment 
of  the  Periodic  Law. 


PERIODIC  REPETITION  OF  PROPERTIES      451 

the  law  of  octaves.  Newlands'  system  of  classification,  al- 
though it  contained  many  of  the  principles  we  use  to-day, 
attracted  little  notice.  Lacking  a  strong  advocate  to  push 
its  claim,  the  new  system  was  soon  forgotten.  In  1869 
Mendelejeff,  a  Russian  chemist,  aroused  great  interest 
in  scientific  circles  by  bringing  forward  a  system  of  clas- 
sification which  for  the  first  time  brought  all  the  elements 
into  a  comprehensive  scheme  of  relationship  based  upon 
their  atomic  weights.  A  few  months  later,  Lothar  Meyer, 
a  German,  put  forward  a  similar  system  which  he  had 
worked  out  independently  of  Mendelejeff.  Although 
Meyer  has  done  much  to  assist  in  classifying  the  elements, 
it  is  now  generally  acknowledged  that  Mendelejeff  is 
entitled  to  the  greater  credit,  and  the  system  we  use 
to-day  bears  the  name  of  the  Russian  chemist.  It  was 
Mendelejeff  who  brought  forward  a  system  which  he 
elaborated  and  successfully  defended  against  the  many 
attacks  made  upon  it. 

493.  Periodic  Law.  —  Beginning    with   lithium,   let   us 
arrange  the  elements  in  the  order  of  their  atomic  weights : 

LITHIUM        GLUCTNITM         BORON        CARBON        NITROGEN        OXYGEN        FLFORINB 

7  9  11 '         12  14  16  19 

Lithium  is  an  element  with  strong  metallic  or  basic  prop- 
erties ;  glucinum,  Gl,  is  less  metallic ;  boron  has  some 
metallic  properties,  but  generally  acts  like  a  non-metal ; 
carbon  forms  weak  acids;  nitrogen  shows  stronger  acid 
properties ;  oxygen  is  characteristically  acid  ;  fluorine,  at 
the  end,  is  the  most  pronounced  acid  element.  Hence, 
the  seven  elements  show  a  gradation  in  properties  from  a 
pronounced  metal  to  an  element  of  strongly  acid  charac- 
ter. A  similar  transition  can  be  shown  for  other  prop- 
erties as  we  pass  from  lithium  to  fluorine.  Thus  the 


452 


THE  PERIODIC  LAW 


II 
u 

o 

-- 


45 


Is       i         il 


A 
OH 


si 


£8 

i      e! 


080 


OH 


1       £1 


Co. 


jr 


2s 


r 


£§ 


«5  CO  tx.  oo  05  O  H 


LONG  AND  SHORT  PERIODS 


453 


properties  seem  to  vary  with  the  atomic  weights,  or,  in 
mathematical  language,  the  properties  are  functions  of 
the  atomic  weights.  Sodium,  the  eighth  element  after 
lithium,  closely  resembles  it,  and  may  be  placed  directly 
beneath  as  the  beginning  of  another  horizontal  row: 


Lithium 
7 
Sodium 
23 

Glucinum 
9 
Magnesium 
24 

Boron 
11 
Aluminum 
27 

Carbon 
12 
Silicon 

28 

Nitrogen 
14 
Phosphorus 
31 

Oxygen 
16 
Sulphur 
32 

Fluorine 
19 
Chlorine 
35.5 

Magnesium  resembles  glucinum  in  its  properties,  and  the 
characteristics  of  boron  recur  modified  in  aluminum. 
That  is,  the  eighth  element  repeats  the  properties  of  the 
one  taken  as  the  first.  Silicon,  then,  should  be  like  car- 
bon, and  phosphorus  should  resemble  nitrogen.  These  we 
know  to  be  facts.  Since  the  properties  recur  or  are  re- 
peated at  regular  intervals,  the  properties  are  said  to 
be  periodic;  or,  as  Mendelejeff  expressed  it,  "a  periodic 
repetition  of  properties  is  obtained  if  all  the  elements  be 
arranged  in  the  order  of  the  atomic  weights." 

494.  Long  and  Short  Periods. — The  table  on  the  opposite 
page  is  arranged  according  to  the  principle  of  classification 
just  given.  Omitting  for  the  present  the  first  vertical 
column  marked  Series  0,  the  seven  elements,  from  lithium 
to  fluorine,  form  a  horizontal  series  known  as  a  short  period. 
The  set  of  elements  from  sodium  to  chlorine  make  the 
second  short  period.  Beginning  in  the  next  line  with 
potassium,  it  is  found  that  the  metallic  properties  do  not 
disappear  so  rapidly  as  in  the  first  and  second  short 
periods.  Manganese,  the  seventh  element,  has  some  well- 
marked  metallic  properties.  Iron  is  not  placed  under  po- 
tassium, but  is  put  in  an  eighth  series  together  with  cobalt 


454  THE  PERIODIC  LAW 

and  nickel.  There  is  a  gradual  increase  in  the  metallic 
properties  as  we  pass  through  these  three  elements  to  the 
more  metallic  copper.  The  elements  from  copper  to  bro- 
mine show  a  gradual  decline  in  the  metallic  properties 
and  an  increase  in  the  acid  properties  until  the  strongly 
acid  element  bromine  is  reached.  Hence  we  have  a  series 
of  seventeen  elements,  beginning  with  potassium  and  end- 
ing with  bromine.  This  is  known  as  a  long  period.  The 
elements  from  rubidium  to  iodine  constitute  the  second 
long  period.  In  this  period  the  elements  of  the  eighth 
series,  ruthenium,  rhodium,  and  palladium,  form  a  bridge 
in  the  transition  of  properties  from 'the  seventh  series  to 
the  first. 

495.  Families  or  Groups  of  Elements. — It  is  evident  from 
the  periodic  nature  of  the  classification  that  all  the  ele- 
ments in  one  of  the  vertical  series  have  certain  resem- 
blances. The  relationship,  however,  is  much  closer  in 
some  cases  than  in  others.  Thus,  in  Series  II,  calcium, 
strontium,  and  barium  are  more  closely  allied  to  each 
other  than  they  are  to  magnesium,  zinc,  cadmium,  and 
mercury.  These  last  four  elements  form  a  closely  re- 
lated group.  That  is,  the  more  closely  related  elements 
are  not  successive,  but  alternate  in  a  vertical  series.  The 
result  of  this  alternate  arrangement  is  to  divide  each 
vertical  series  into  two  families  or  groups.  In  Series  VI, 
chromium  and  molybdenum  are  in  one  family,  while  sul- 
phur, selenium,  and  tellurium  form  the  other.  The  halo- 
gen elements,  chlorine,  bromine,  and  iodine,  in  Series 
VII,  afford  one  of  the  best  examples  of  a  closely  related 
group.  Lithium,  potassium,  rubidium,  and  caesium,  in 
Series  I,  are  a  group  of  soft,  waxy  metals  of  high  luster 
and  low  boiling  points.  They  decompose  water  readily, 
forming  caustic  bases.  A  study  of  their  properties  shows 


FAMILIES   OR    GROUPS   OF  ELEMENTS 


455 


that  a  gradual  transition  in  properties  accompanies  the 
increase  in  atomic  weights. 

A  similar  variation  in  properties  in  accordance  with 
the  increase  in  atomic  weight  in  a  vertical  series  is  well 
brought  out  in  the  study  of  the  elements  of  the  halo- 
gen group.  At  the  head  of  each  vertical  series  are  placed 
some  general  formulas  for  the  oxides  and  hydroxides  of 
the  elements  in  the  series  beneath.  R  is  the  general  sym- 
bol for  an  atom  of  the  element  under  consideration.  Thus 
in  Series  I  the  general  formula  of  the  oxide  is  R2O,  and 
we  have  the  oxides  Li2O,  Na2O,  K2O,  Cu2O,  and  so  on. 

These  general  formulas  may  be  extended  to  include 
other  compounds,  as  the  chloride,  nitrate,  and  sulphate: 


SERIES   I 


SERIES  II 


Oxide 


FORMULA 

R20 


ILLUSTRATION 

FORMULA 

ILLUSTRATION 

K20 

R2O2 

CaO 

KOH 
KC1 

(=2RO) 
R(OH)2 
RC12 

Mg(OH)2 
HgCl2 

Hydroxide  ROH 

Chloride  RC1 

Nitrate  RNO3         KNO3         R(NO3)2        Zn(NO3), 

Sulphate  R2SO4         K2SO4        RSO4  BaSO4 


Oxide 

Hydroxide 

Chloride 

Nitrate 

Sulphate 


SERIES  III 

FORMULA 


R(OH)8 

RC13 

R(N03)3 


ILLUSTRATION 

A12O3 

A1(OH)3 

A1C13 

A1(N03)3 
A12(S04)3 


It  can  be  seen  from  the  study  of  these  general  formulas 
that  there  is  a  regular  increase  in  valence  as  we  proceed 
from  the  first  series  to  the  seventh. 


456  THE  PERIODIC  LAW 

496.  Position  of  the  Inert  Gases  and  of  Hydrogen.  —  With 
the  discovery  of  argon  and  other  inert  gases,  considerable 
discussion  arose  as  to  their  proper  place  in  the  periodic 
system.     Since  no  compounds  of  these  elements  are  known, 
they  cannot  be  properly  placed  in  any  one  of  the  vertical 
series.     Accordingly  it  has  been  deemed  best  to  form  a 
separate  vertical  series  for  these  elements  at  the  beginning 
of  the  classification,  and  mark  it  Series   0.       Including 
these  inert  elements,  the  first  two  short  periods  have  eight 
elements  each,  while  the  first  long  period  has  eighteen. 

It  will  be  noticed  that  hydrogen  is  not  placed  in  the 
table  given  on  page  452.  Since  it  has  the  smallest  atomic 
weight,  its  natural  position  would  be  the  beginning  of  the 
classification.  If,  however,  it  were  placed  in  Series  0, 
it  would  be  classed  with  the  inert  elements  from  which  it 
differs  decidedly  in  its  properties.  A  similar  difficulty 
would  arise  if  hydrogen  was  placed  in  Series  I,  which  con- 
tains the  alkali  metals.  The  position  of  hydrogen  is  so 
uncertain  that  it  is  left  out  of  many  periodic  tables. 

497.  Significance  of  Vacant  Spaces  in  Table.  —  It  will  be 
noticed  that  the  series    of  elements  is    almost  complete 
until  the  atomic  weight  of  145  is  reached,  while  among 
the  elements  of  a  greater  atomic  weight  many  vacancies 
exist.       Considerable   speculation    has   arisen    as   to   the 
meaning  of  these  gaps.     Perhaps  in  time  other  elements 
will  be  discovered  to  fill  these  blanks. 

498.  Value  of  the  Periodic  System.. —  Mendelejejfs  system 
has  been  of  great  value  in  predicting  the  discovery  of  new 
elements.     In  fact,  in  the  years  immediately  following  the 
announcement  of  the  law,  when  its  validity  was  so  much 
questioned,  the  fulfillment  of  Mendelejeff's  predictions  as 
to  the  existence  and  properties  of  elements  then  unknown 


VALUE   OF   THE  PERIODIC  SYSTEM 


457 


gave  striking  evidence  of  the  correctness  of  the  new  system 
of  classification.  The  table  following  shows  the  predic- 
tions and  their  verification  in  the  case  of  an  element  which 
Mendelejeff  called  eka-aluminum,  and  which  is  now  known 
as  gallium  : 


PROPERTIES 

PREDICTED 

DISCOVERED 

Atomic  weight 

About  69 

69.9 

Melting  point 

Low 

30.1° 

Specific  gravity 

About  5.9 

5.93 

Action  of  air 

None 

Slightly  oxidized  at  red 

heat 

Action  on  water 

Decomposes  at  red  heat 

Decomposes      at      high 

temperatures 

The  predictions  by  Mendelejeff  and  their  subsequent  veri- 
fication were  equally  striking  in  the  cases  of  eka-boron 
(scandium)  and  eka-silicon  (germanium). 

The  second  use  of  the  classification  is  in  the  adjustment 
and  revision  of  atomic  weights.  In  the  early  days  of  the 
classification  many  of  the  elements  were  improperly 
placed.  It  was  suggested  that  this  might  be  due  to  in- 
correct values  for  the  atomic  weights.  This  led  to  more 
accurate  determinations  of  the  atomic  weights.  In  many 
cases  results  were  obtained  which  permitted  the  ele- 
ments to  be  placed  in  the  table  according  to  their 
proper  relationships.  Chemical  research  has  been  greatly 
stimulated  by  these  revisions  of  atomic  weights. 

The  development  of  a  systematic  study  of  the  elements  has 
been  the  greatest  service  of  the  periodic  law.  A  knowledge 
of  relationships  has  simplified  the  determination  of  the 
physical  and  chemical  properties  not  only  of  the  elements 
but  of  their  compounds.  Although  the  system  of  Men- 


458  THE  PERIODIC  LAW 

delejeff  is  not  perfect,  and  no  exact  numerical  relations 
have  been  found,  the  periodic  classification  is  of  great  aid 
to  the  student  of  descriptive  chemistry. 

SUMMARY 

The  principle  of  the  Mendelejeff  classification  of  the  elements  is 
that  "  a  periodic  repetition  of  properties  is  obtained  if  all  the 
elements  be  arranged  in  the  order  of  the  atomic  weights." 

While  the  elements  in  the  horizontal  series  show  a  gradual 
transition  in  properties,  the  most  closely  related  families  or  groups 
are  arranged  alternately  in  the  vertical  series. 

The  Periodic  System  has  been  of  great  value  in  (a)  predicting 
the  discovery  of  new  elements,  (b)  the  adjustment  and  revision  of 
atomic  weights,  (c)  the  development  of  a  systematic  study  of  the 
elements. 

EXERCISES 

1.  Show  that  there  is  in  the  second  short  period  a  transition 
from  a  strongly  metallic  element  to  a  pronounced  acid  element. 

2.  Show  by  illustrations  that  the  Mendelejeff  classification 
is  a  periodic  one. 

3.  Using  symbols,  indicate  two  families  of  elements  in  each 
of  the  following  vertical  series  —  II,  IV,  VI. 

4.  Give  formulas  for  the  oxide,  hydroxide,  sulphate,  nitrate, 
and  chloride  of  indium  (In). 

5.  Show  that  the  placing  of  the  inert  elements  as  Series  0 
does  not  alter  the  periodic  nature  of  the  table. 

6.  What  two  uses  of  the  table  were  of  great  value  in  securing 
its  acceptance  by  chemists  ? 

7.  How  may  a  student  use  the  table  profitably  in  the  study 
of  chemistry  ? 


CHAPTER   XXXVIII 
INDUSTRIAL  CARBON  COMPOUNDS 

499.  Organic  Chemistry.  —  The  term  organic  chemistry 
owes  its  origin  to  the  notion  that  a  force  different  from 
that  governing  the  mineral  kingdom  was  necessary  for 
the  formation  of  nearly  all  compounds  produced  by  plants 
and  animals.  This  belief  was  overthrown  by  Wohler  in 
1828,  but  organic  chemistry  is  still  the  name  commonly 
applied  to  the  study  of  the  carbon  compounds.  Carbon 
unites  with  other  elements  to  form  a  very  large  number 
of  compounds,  most  of  which  have  a  complex  structure.  As 
a  rule,  carbon  compounds  are  only  slightly  ionized  by  water. 


460  INDUSTRIAL    CARBON  COMPOUNDS 

500.  Sources.  —  Coal,    wood,    and   petroleum    are    the 
sources  of  a  multitude  of  useful  carbon  compounds.     Cel- 
lulose, the  chief  constituent  of  the  cell  walls  of  plants,  is 
extensively  employed  in  making  paper,  guncotton,  collo- 
dion, and  celluloid.     The  fat  of  cattle,  hogs,  sheep,  fish, 
and  whales  is  used  in  the  manufacture  of  a  large  number 
of  substances.     Useful  oils  and  fats  are  obtained  from  the 
seeds  of  cotton,  hemp,  and  flax  ;  from  the  fruit  of  the  oil 
palms,  the  cocoanut  palm,  and  the  olive  tree.     In  fact,  a 
great  variety  of  plants  furnish  valuable  oils.     Milk  is  the 
source  of  butter,  cheese,   casein,  and  milk  sugar,  all  of 
which  are  of  great  industrial  importance.     Starch  is  ob- 
tained   in   this  country   chiefly   from   corn  ;    sugar  from 
sugar  cane,  beets,  and  the  sugar  maple. 

501.  Destructive  Distillation. — When  soft  coal  is  heated 
in  the  absence  of  air,  volatile  substances  pass  off,  and  coke 
is  left  as  a  residue.     A  similar  change  takes  place  when 
either  wood  or  bone  is  heated  without  air.     The  process 
of  decomposing  complex  organic  substances  by  heat  in 
closed  vessels  and  condensing  the  vapor  of  the  liquid  prod- 
ucts, is  termed  destructive  distillation.      On  account  of  the 
valuable  substances  obtained  by  the  destructive  distillation 
of  soft  coal  and  wood,  these  operations  are  carried  out  on 
a  large  scale. 

502.  The  Destructive  Distillation  of  Soft  Coal  is  an  exten- 
sive industry  for  obtaining  illuminating  gas,  coke,  and 
valuable  by-products,  including  coal    tar   and   ammonia. 
From  coal    tar,    a  great  variety  of  useful  substances  is 
made. 

503.  niuminating  Gas.  —  The  manufacture  of  enriched" 
water  gas  and  of  producer  gas  has  been  treated  (§§  335 


ILLUMINATING   GAS 


461 


and  336).  The  making  of  illuminating  gas  from  soft 
coal  begins  with  the  destructive  distillation  of  the  coal. 
This  is  carried  on  in  long  retorts  placed  in  either  a  hori- 
zontal, an  inclined,  or  better,  a  vertical  position,  and 
heated  by  coke  or  by  producer  gas  (Fig.  144).  Con- 
nected with  each  retort  is  a  pipe  which  conveys  the  hot 
gases  from  the  retorts  to  a  large  pipe,  called  the  hydraulic 
main,  through  which  water  flows.  The  gases  coming 
from  the  retorts  are  discharged  under  the  water,  which 


Condenser 


Scrubber 


FIG.  144.  —  MANUFACTURE  OP  ILLUMINATING  GAS. 

serves  as  a  seal  to  prevent  the  backward  flow  of  gas, 
when  a  retort  is  opened  and  the  pressure  thereby  de- 
creased. 

From  the  hydraulic  main,  the  hot  gases  pass  to  a  con- 
denser, where  cooling  by  air  or  water  takes  place  and 
some  of  the  tar  is  deposited.  On  leaving  the  primary 
condenser,  the  gas  passes  to  a  tar  extractor,  which  removes 
the  remainder  of  the  tar  by  causing  the  gas  containing 
tar  vapor  to  impinge  against  sheets  of  metal.  Next  to  the 
tar  extractor  is  placed  an  exhauster,  which  is  used  to  main- 
tain the  desired  pressure  in  the  retorts  and  to  force  the 


462 


INDUSTRIAL   CARBON  COMPOUNDS 


gas  through  a  series  of  scrubbers  and  purifiers  into  a  gas 
holder.  The  tar  extractor  and  exhauster  are  not  shown 
in  the  figure. 

The  scrubbers  are  horizontal  cylinders,  each  of  which  is 
divided  by  several  vertical  partitions.  Through  the  cen- 
ter of  each  scrubber  passes  a  horizontal  shaft  carrying 
a  series  of  paddle  wheels.  As  the  paddle  wheels  revolve, 
the  blades  at  one  instant  dip  in  the  absorbing  liquid  of 
the  purifier,  and  the  next  instant  present  a  large  wet  sur- 
face to  the  gas  passing  through  the  apparatus.  By  the 
use  of  scrubbers,  naphthalene,  cyanogen,  and  ammonia  are 
absorbed.  Between  the  cyanogen  scrubber  and  the  am- 
monia washer  is  a  secondary  condenser,  which  is  used  to 
cool  the  gas  so  that  any  ammonia  it  contains  will  be 
absorbed  by  the  water  flowing  through  the  ammonia 
scrubber.  After  the  removal  of  ammonia,  the  gas  is  con- 
ducted through  a  series  of  purifiers  to  remove  hydrogen 
sulphide.  The  purifiers  contain  layers  of  wood  shavings 
coated  with  ferric  oxide.  The  purified  gas  is'  measured 

by  a  large  gas  meter  and  stored 

in  a  gas  holder. 

504.  The  Destructive  Distillation 
of  Wood  is  carried  on  in  a  retort 
(Fig.  145)  connected  with  a  con- 
denser. The  primary  products 
of  the  distillation  are  gas,  py- 

roligneous  acid,  wood  tar,  and  charcoal.  From  the  pyro- 
ligneous  acid,  several  valuable  compounds  are  obtained. 
Wood  alcohol,  acetic  acid,  and  acetone  are  some  of  them. 

505.  Boneblack  is  the  residue  remaining  after  bones  have 
been  heated  in  a  retort.  The  volatile  matter  produced 
during  the  process  is  sometimes  collected  and  worked  into 


FIG.  145. 


DISTILLATION  OF  PETROLEUM  463 

useful  substances.  Before  the  heating  in  the  retort  takes 
place,  grease  is  frequently  removed  from  the  bones  by  a 
suitable  solvent,  and  gelatine  is  sometimes  prepared  by 
boiling  them  in  water  under  pressure. 

506.  Fractional  Distillation.  —  When  a  mixture  of  water 
and  alcohol  is  distilled,  the  liquid  commences  to  boil  at  a 
temperature  near  78°  C.,  the  boiling  point  of  alcohol.     As 
the  distillation  continues,  the  boiling  point  rises  until  a 
temperature  a  little  above  that  of  boiling  water  is  reached. 
While  the  distillation  is  going  on,  the  distillate  is  gen- 
erally separated  into  fractions  by  collecting  the  distillate 
in  different  vessels.     One  fraction  of  the  distillate  is  col- 
lected during  a  definite  rise  in  the  temperature  of  the 
boiling  liquid,  a  second  portion  of  the  distillate  during 
another  rise,  and  so  on.     The  fraction  first  collected  con- 
tains a  large  percentage  of   alcohol,  while  the  fractions 
collected    during   the  latter  part  of  the  process  will  be 
composed  chiefly  of  water.     By  repeating  the  distillation 
of  the  fractions,  the  original  mixture   can    be  separated 
into  two  parts,  one  containing.  95  per  cent  alcohol  and 
the  other  nearly  pure  water. 

Fractional  distillation  is  the  partial  separation  of  two  or 
more  miscible  liquids  by  distilling  the  mixture  and  col- 
lecting fractions  of  the  distillate  in  different  vessels. 

507.  Distillation  of  Petroleum.  —  Petroleum  may  be  sep- 
arated into  useful  substances  by  fractional  distillation,  but 
oil  refiners  generally  combine  fractional  distillation  with 
a  kind  of  destructive  distillation.     As  the  distillation  of 
the  petroleum  proceeds,  the  boiling  point  of  the  liquid  in 
the  still  (Fig.  146,  A)  rises.     When  a  portion  of  the  vapor 
is  condensed  and  made  to  drop  into  the  hot  oil  in  the  still, 
it  at  once  becomes  superheated  and  its  compounds  decom- 


464 


INDUSTRIAL    CARBON   COMPOUNDS 


pose  into  other  compounds  having  a  lower -boiling  point. 
A  little  carbon  separates  during  the  operation.  The  de- 
composition of  the  higher  compounds  of  the  oil  is  termed 
cracking. 

The  distillate  from  the  crude  oil  is  first  separated  into 
three  fractions.  This  is  accomplished  by  two  air-cooled 
condensers,  B  and  (7,  from  which  the  successive  fractions 


/ 

Or  Q  O  Q 

g 

FIG.  146.  —  FRACTIONAL  DISTILLATION  OF  CRUDE  PETROLEUM. 

pass  through  three  coils  of  pipe,  immersed  in  a  tank  of 
water,  D,  in  which  the  condensing  process  is  completed. 
The  fractions  are  run  into  different  storage  tanks  by 
means  of  the  distributing  sink,  E.  Coke  is  left  in  the 
still.  Each  of  the  three  fractions  of  the  distillate  is  then 
redistilled,  and  treated  so  as  to  yield  substances  for  which 
there  is  a  demand.  By  varying  the  treatment  of  the 
petroleum  during  distillation,  and  by  distilling  under 
reduced  pressure,  the  products  obtained  can  be  varied. 
Gasoline,  naphtha,  benzine,  kerosene,  gas  oils,  lubricat- 


Robert  Kennedy  Duncan  (1868-1914)  was  born  at  Brantford, 
Ontario.  From  1910  to  1914  he  was  director  of  the  Department 
of  Industrial  Research  of  the  University  of  Pittsburgh,  and  was 
the  founder  of  the  unique  system  of  cooperation  between  science 
and  industry  in  operation  at  the  Mellon  Institute  of  the  University 
of  Pittsburgh.  He  was  a  man  who  possessed  great  literary  ability 
and  who  narrated  the  great  discoveries  of  modern  physical  science 
in  language  easily  understood  by  the  layman,  having  a  style 
as  fascinating  as  that  of  a  novelist.  He  was  the  author  of  "The 
New  Knowledge,"  "The  Chemistry  of  Commerce,"  and  "Some 
Chemical  Problems  of  To-day." 


FERMENT  A  TION 


465 


ing  oils,  vaseline,  and  paraffin  are  the  more  important' 
substances  obtained  from  crude  petroleum.  Paraffin  is 
separated  from  a  fraction  of  the  petroleum  distillate  by 
artificial  chilling. 

508.  Fermentation.  —  The  term  "  yeast "  is  applied  to  cul- 
tures of  yeast  plants.  There  are  several  varieties  of 
yeast;  these  plants  are  all  microscopic  in  size  (Fig.  147) 
and  secrete  powerful  catalytic  agents  called  enzymes. 
The  most  important  enzyme,  called  zymase,  has  the  power 


a  b 

FIG.  147.  —  YEAST  CELLS,  HIGHLY  MAGNIFIED. 
a,  living;  b,  dead.   . 

of  converting  fermentable  sugars  into  alcohol  and  carbon 
dioxide. 

When  yeast  is  placed  in  a  warm,  dilute  solution  of 
molasses,  bubbles  of  a  gas,  carbon  dioxide,  soon  cause  the 
liquid  to  foam  and  alcohol  is  generated.  Fermentation  is 
a  chemical  change  brought  about  by  living  organisms  or 
by  catalytic  agents,  called  enzymes,  secreted  by  them. 
Gases  are  frequently  evolved  during  fermentations,  so 
that  the  liquid  becomes  covered  with  froth.  When  pre- 
serves ferment,  they  are  commonly  said  to  "work."  In 
the  home,  yeast  is  used  to  generate  carbon  dioxide  in  the 
dough  of  yeast  bread.  The  bubbles  of  gas  make  the 
bread  light  and  more  digestible.  The  alcohol  produced  is 
driven  off  when  the  bread  is  being  baked. 


466  INDUSTRIAL   CARBON  COMPOUNDS 

509.  Production  of  Alcohol.  — Ordinary  alcohol  is  made 
in  large  quantities  from  grain  or  potatoes  by  the  process 
of  fermentation.  Both  of  these  substances  contain  a  large 
quantity  of  starch.  This  is  converted  into  maltose, 
C12H22On  •  H2O,  by  diastase,  an  enzyme  contained  in  the 
malt  (§  510)  that  is  added.  The  malted  mixture  is  agitated 
with  water  at  63°C.  The  liquid  is  then  cooled,  diluted 
with  water,  and  yeast  added.  The  zymase  formed  by  the 
yeast  brings  about  the  following  reaction  with  the  sugars 
maltose  : 

Ci2H22Ou  •  H20  — ^  4  C2H6OH  +  4  CO2 

When  molasses  (cane  sugar)  is  used,  the  process  is 
similar,  except  that  no  malt  is  necessary.  The  cane  sugar 
is  first  converted  into  dextrose  and  levulose  by  a  ferment 
known  as  invertase,  also  produced  by  the  yeast  plant. 

O^H^OH  +  H20  — ^  C6H1206  +  C6H1206 

cane  sugar  dextrose  levulose 

Then  the  zymase  from  the  yeast  brings  about  the  alcoholic 
fermentation  of  the  two  simple  sugars  : 

C6H1206  -+  2  C2H5OH  +  2  CO2 

dextrose  or 
levulose 

The  alcohol  is  separated  from  the   resulting  solution  by 
repeated  distillations. 


510.  Alcoholic  Beverages. — Beer  is  the  product  obtained 
by  the  fermentation  of  malt.  Barley  is  placed  in  a  warm 
moist  room  until  the  kernels  germinate.  When  the  root- 
let has  grown  to  be  two  thirds  the  length  of  the  kernel, 
the  grain  is  heated  to  stop  the  growth.  During  the  ger- 
mination the  starch  in  the  barley  is  converted  into 
maltose.  The  malt  thus  obtained  is  ground  and  boiled 


VINEGAR  467 

with  water.  Yeast  is  added  to  ferment  the  malt  sugar. 
The  fermented  liquor  is  filtered  and  water  added  to  pro- 
duce a  beer  or  ale  of  the  desired  concentration.  .  Rice  and 
glucose  are  often  used  to  replace  barley.  Hops  and  other 
flavoring  materials  are  also  utilized.  Beer  contains  from 
3  to  5  per  cent  alcohol  in  addition  to  soluble  materials 
from  the  grain. 

Wines  are  produced  by  the  fermentation  of  fruit  juices 
which  contain  grape  sugar  (glucose).  After  fermenting, 
the  liquor  is  allowed  to  settle  and  the  clear  liquid  is  drawn 
off.  The  wine  thus  produced,  in  addition  to  7—15  per 
cent  of  alcohol,  contains  soluble  materials  derived  from 
the  fruit  or  produced  in  the  fermeutationo  Whisky  is 
made  by  distilling  a  beer  obtained  from  rye  or  corn,  so 
that  the  percentage  of  alcohol  is  increased  to  about  25-45 
per  cent.  Brandy,  resulting  from  the  distillation  of  wine, 
may  contain  50  per  cent  alcohol  5  and  rum  and  gin,  derived 
from  fermenting  molasses,  possess  about  30  and  40-80  per 
cent  respectively.  All  of  these  distilled  liquors  contain 
minute  quantities  of  flavoring  materials  and  traces  of 
acid. 

511.  Vinegar. — Dilute  solutions  of  alcohol,  such  as  are 
represented  in  weak  wines,  or  hard  cider,  when  exposed 
to  the  air,  undergo  a  fermentation  which  results  in  the 
oxidation  of  alcohol  to  acetic  acido  Vinegar  is  the  liquid 
that  results  from  this  action;  it  is  a  dilute  solution  of 
acetic  acid  containing  substances  that  give  it  color  and 
modify  its  flavor.  Vinegar  is  sometimes  manufactured  by 
what  is  called  the  quick  vinegar  process.  Dilute  alcohol, 
to  which  a  certain  amount  of  beer  or  malt  extract  has 
been  added,  is  allowed  to  trickle  over  a  mass  of  wood 
shavings  that  have  been  previously  treated  with  vine- 
gar in  order  to  insure  the  presence  of  the  fermenting  or- 


468  INDUSTRIAL   CARBON  COMPOUNDS 

ganism.    The  porous  mass  of.  shavings  makes  possible  free 
contact  with  air,  which  furnishes  the  necessary  oxygen. 

512.  Soap  Making. — No  technical  process  depends  more 
upon  the  skill  of  the  operator  than  the  manufacture  of 
soap.  In  general,  soaps  may  be  classed  as  boiled,  semi- 
boiled,  or  cold  process.  Boiled  soaps  are  produced  by 
boiling  fats  with  sodium  hydroxide  and  carbonate.  They 
are  often  called  settled  or  grain  soaps  because,  during  the 
process  of  manufacture,  the  glycerine  is  separated  from 
the  soap.  Semi-boiled  soaps  contain  all  of  the  glycerine 
derived  from  the  fats.  Cold  process  soaps  are  formed  by 
the  direct  combination  of  the  fat  and  alkali,  without  the 
aid  of  external  heat. 

Most  hard  soaps  used  for  household  purposes  are  boiled 
soapso  Soap  is  made  in  large  iron  kettles,  fitted  with  two 
sets  of  steam  pipes;  one,  a  closed  coil  to  supply  heat,  and 
the  other  an  open  coil  to  deliver  steam  through  the  charge 
to  keep  it  stirred.  Melted  fat  and  about  one  fourth  the 
quantity  of  alkali  required  for  complete  saponification  are 
run  into  the  kettle  and  the  steam  turned  on.  The  con- 
centration of  the  alkali  is  regulated  by  the  kind  of  fat 
used.  When  the  mixture  has  become  homogeneous,  a  more 
concentrated  alkali  is  added  and  the  boiling  continued 
until  a  sample  shows  that  the  product  has  the  desired  con- 
sistency0  Salt  is  then  added,  and  the  soap,  being  insoluble 
in  brine,  separates.  The  kettle  is  allowed  to  remain  quiet 
for  several  hours  and  the  soap  collects  on  top  of  the  liquid. 
This  liquid  is  called  spent  lye.  It  contains  glycerine,  water, 
salt,  and  impurities  from  the  alkali  and  fat.  The  spent 
lye  is  drained  off,  the  salt  and  glycerine  are  separated  from 
it,  and  the  layer  of  soap  is  boiled  with  sufficient  alkali  to 
complete  the  saponification0  During  this  boiling,  rosin 
is  sometimes  added.  Pure  rosin  soaps  have  strong 


STARCH 


469 


cleansing   properties,    but    are   too   soft   and   sticky   for 
general  use. 

The  soap  when  taken  from  the  kettle  is  often  mixed  with 
one  or  more  of  various  fillers,  such  as  sodium  carbonate, 
borax,  and  sodium  silicate.  Coloring  materials  and  per- 
fumes may  also  be  added.  Soaps  that  float  are  made  light 
by  having  air  forced  through  them  while  they  are  in  the 
pasty  condition.  If  a  good  quality  of  soap  is  dissolved  in 
alcohol  and  then  dried,  a  transparent  soap  is  obtained. 
Sugar  and  glycerine  are  often  used  in  the  manufacture 
of  transparent  soaps.  Most  soap  powders  consist  essen- 
tially of  hard  soap,  ground  with  sodium  carbonate. 

513.  Starch.  —  Starch  is  found  as  granules  in  the  cells 
of  plants.  These  granules  consist  of  a  wall  of  starch  cel- 
lulose within  which  is  soluble  starch.  Starch  is  insoluble 
in  cold  water,  but  boiling  water  causes  the  walls  of  the 
starch  granules  to  burst,  and  the  soluble  starch  enters 
solution.  Much  starch  is  obtained  from  corn  and  potatoes. 


PRODUCTS  OBTAINED  FROM  CORN 

Corn  Kernel 


Germ 

Endosperm 

Hull 

Corn  Oil 
Rubber  Substitute 

Oil  Cake 
Cattle  Feed 

Sta 

rch             Gluten 
Cattle  Feed 

Cattle  Feed 

N.  P.  Corn  Syrup 
Export  Corn  Syrup 
70  Sugar 
80  Sugar 

Anhydrous  Sugar 
Table  Syrups 


White  Dextrine 
Sp.  White  Dextrine 
Canary  Dextrine 
Sp.  Dark  Canary 
American  Guni 
British  Gum 


Pearl  Starch 

Powdered  Starch 

Laundry  Starch 

Thin  Boiling  Confectioners 

Thin  Boiling  Laundry 

Corn  Starch 

Ivory  Starch 

Srits 


4TO 


INDUSTRIAL   CARBON  COMPOUNDS 


No  matter  what  the  source,  the  method  of  preparing 
starch  is  the  same.  The  material  is  crushed,  then  macerated 
with  water,  and  the  milk-colored  liquid  filtered  through 
cloth  fine  enough  to  prevent  all  besides  the  water  and 
starch  from  passing.  The  starch  is  allowed  to  settle  to 
the  bottom  of  the  containing  vessel,  from  which  it  is  after- 
wards removed  and  dried. 


FIG.   148.  —  BRINGING  SUGAR  CANE  TO  THE  FACTORY. 

514.  Sugar  Manufacture  and  Refining.  —  S ugar  is  obtained 
from  the  juices  of  the  sugar  cane  and  beets.  After  ex- 
traction, slaked  lime  is  added  to  the  juice  to  prevent  fer- 
mentation and  to  precipitate  the  albuminous  substances 
coming  from  the  plant  cells.  The  solution  is  then  fil- 
tered through  cloth  and  evaporated  in  a  vacuum  pan  at  a 
temperature  of  about  66°  C.  If  the  evaporation  were  car- 
ried on  under  ordinary  pressure,  the  temperature  would 
become  sufficiently  high  to  convert  the  saccharose  into  a 
mixture  of  glucose  and  fructose. 


SUGAR   REFINING  471 

As  soon  as  a  sample  taken  from  the  vacuum  pan  shows 
that  sugar  will  crystallize  when  the  syrup  cools,  the  solu- 
tion is  removed  from  the  pan  and  allowed  to  cool.  The 
crystals  are  dried  in  centrifugal  machines.  The  product 
obtained  is  usually  raw  sugar  which  must  be  refined  be- 
fore being  placed  on  the  market.  Nearly  all  sugar  refin- 
eries are  in  the  northern  states. 

The  raw  sugar  is  dissolved  in  large  vats  and  the  syrup 
pumped  to  the  top  of  high  buildings,  where  it  is  mixed 
with  lime  and  a  little  monocalcium  phosphate  to  remove 
any  albuminous  material  that  may  have  been  left  in  the 
sugar.  The  syrup  is  then  filtered  through  long  sacks, 
called  bag  filters,  to  remove  the  coarse  impurities  that  are 
suspended  in  the  solution.  After  this,  the  liquid  is  fil- 
tered through  boneblack  to  remove  the  coloring  matter. 
The  purified  syrup  is  boiled  in  vacuum  pans  as  in  the  case 
of  raw  sugar. 

Crystals  of  pure  sugar  have  a  pale,  yellowish  tint.  As 
most  people  are  ignorant  of  this  fact  and  demand  that  a 
white  sugar  be  sold  them,  the  sugar  refiners  add  some 
blue  pigment  to  the  sugar,  for  example  ultramarine.  The 
blue  counteracts  the  yellow  and  causes  the  sugar  to  appear 
white. 

SUMMARY 
Organic  chemistry  is  the  chemistry  of  the  carbon  compounds. 

Carbon  compounds  are  derived  chiefly  from  petroleum,  coal,  and 
plants. 

Destructive  distillation  is  the  conversion  of  complex  substances 
into  simpler  substances  by  means  of  heat  in  the  absence  of  air. 
Volatile  substances  pass  off  and  a  solid  residue  is  left. 

Fractional  distillation  is  the  more  or  less  complete  separation 
of  a  mixture  into  its  constituents  by  making  use  of  the  different 


472  INDUSTRIAL   CARBON  COMPOUNDS 

temperatures  at  which  the  ingredients  boil  and  their  vapors  con- 
dense. 

Alcohol  is  partially  separated  from  water  by  fractional  distillation. 

Gas,  wood  alcohol,  acetone,  acetic  acid,  and  charcoal  are  im- 
portant substances  resulting  from  the  destructive  distillation  of 
wood. 

Illuminating  gas,  ammonia,  tar,  and  coke  are  some  of  the  sub- 
stances obtained  by  the  destructive  distillation  of  soft  coal. 

Gasoline,  naphtha,  benzine,  kerosene,  vaseline,  and  paraffin  are 
obtained  from  petroleum. 

Fermentation  is  a  chemical  change  brought  about  by  living 
organisms  or  by  catalytic  agents  secreted  by  them. 

An  enzyme  is  a  catalytic  agent  secreted  by  a  living  organism. 

Several  of  the  sugars  are  converted  into  alcohol,  and  alcohol  is 
converted  into  acetic  acid  by  processes  of  fermentation. 

Soap  is  made  by  the  reaction  between  sodium  or  potassium 
hydroxide,  on  the  one  side,  and  animal  or  vegetable  oils  and  fats, 
on  the  other  side. 

Starch  is  formed  in  the  cells  of  plants.  It  occurs  in  small 
granules,  which  are  readily  brought  into  suspension  by  stirring  with 
water  and  thus  separated  from  the  plant  tissues. 

Sugar  is  generally  obtained  from  the  sap  of  the  sugar  cane  or 
from  the  sugar  beet.  The  sugar  solutions  are  evaporated  to 
crystallization  in  vacuum  pans.  The  crude  sugar  is  dissolved  in 
water  and  the  solution  passed  through  a  boneblack  filter  to  remove 
the  coloring  matter. 

EXERCISES 

1.  Name   five   organic  substances   used  in  the   home   and 
mention  a  natural  source  of  each. 

2.  What  is  the  meaning  of  destructive  distillation  ? 


EXERCISES  473 

3.  Mention  important  substances  resulting  from  the  destruc- 
tive distillation  of  soft  coal.     From  distillation  of  wood. 

4.  Give  the  important  steps  in  the  manufacture  of  illumi- 
nating gas  from  soft  coal. 

5.  What  are  four  important  products  obtained  during  the 
manufacture  of  illuminating  gas  from  soft  coal  ? 

6.  What  is  fractional  distillation  ? 

7.  Are  gasoline  and  kerosene  chemical  compounds  ?     Why 
do  you  think  so  ? 

8.  How  is  paraffin  obtained  from  petroleum  ? 

9.  What  is  the  meaning  of  the  term  "  fermentation  "  ? 

10.  Name  three  important  substances  produced  by  fermen- 
tation. 

11.  How  is  alcohol  made  from  potatoes  ? 

12.  What  important  chemical  changes  take  place  when  sweet 
cider  changes  to  vinegar  ? 

13.  How  is  soap  made  ? 

14.  What  are  the  principal  constituents  of  soap  powders  ? 

15.  Why  is  not  boiling  water  used  to  prepare  starch  from 
corn? 

16.  Name  three  important  substances  obtained  from  corn. 

17.  What  substance  is  used  to  remove  the  coloring  matter 
from  crude  sugar  ? 

18.  Why  are  sugar  solutions  boiled  in  vacuum  pans  ? 


CHAPTER   XXXIX 

CLASSES  OF  CARBON  COMPOUNDS 

515.  Structural  Formulas.  —  Little  advance  was  made  in 
the  study  of  carbon  compounds  until  chemists  began  to 
represent  the  arrangement  of  the  atoms  in  a  molecule  by 
structural  formulas.     A  structural  formula  may  be  con- 
sidered as  a  map  of  the  molecule. 

516.  Reason  for  the  Large  Number  of  Carbon  Compounds.  — 

Atoms  of  nitrogen,  to  a  limited  extent,  have  the  power  of 
uniting  with  other  atoms  of  nitrogen,  forming  nuclei,  to 
which  other  elements  attach  themselves.  A  similar  state- 
ment is  true  in  the  cases  of  several  other  elements.  Car- 
bon has  this  power  to  an  almost  unlimited  extent.  The 
ability  of  carbon  atoms  to  unite  with  other  carbon  atoms 
to  form  stable  nuclei,  to  which  atoms  of  other  elements 
join,  accounts  for  the  multitude  of  carbon  compounds 
known  to  exist. 

517.  Hydrocarbons. — It  is  customary  to  commence  the 
study  of  the  carbon  compounds  with  a  consideration  of 
compounds  containing  hydrogen  and  carbon  only,  that  is, 
the  hydrocarbons. 

Methane  or  marsh  gas  is  the  hydrocarbon  having  the 
simplest  structure.  Its  molecule  contains  one  carbon 
atom  in  combination  with  four  hydrogen  atoms.  In 
structural  formulas,  the  valences  of  the  elements  con- 
sidered are  represented  by  dashes.  The  valence  of  car- 
bon in  nearly  all  of  its  compounds  is  four  and  the 

474 


PARAFFIN  SERIES  475 


'•4- 


valence  of  the  hydrogen  atom  is  one.  — C —  represents 
the  carbon  atom  and  shows  its  valence.  H —  shows  that 

T     v 

the  valence  of  the  hydrogen  atom  is  one.     H — C— H  is 

H 

the  structural  formula  for  methane  and  shows  that  four 
hydrogen  atoms  having  a  valence  of  one  are  united  to  one 
carbon  atom  having  a  valence  of  four.  When  two  atoms 
of  caVbon  are  joined  by  a  single  valence  bond,  we  obtain 

the   nucleus  — C — C — .     The  hydrogen  compound   con- 

I     I  inJ     Xfa&lfrjr1?. 

H    H 

I  I  ^          -*•„ 

taining    this    nucleus    is    H — C — C — H,    ethane.     In   a 

H     H 

similar  way,  the  chain  of  carbon  atoms  might  be  extended 
and  formulas  for  several  members  of  the  series  derived. 

518.  Paraffin  Series.  —  The  following  table  (p.  47§)  gives 
the  names,  formulas,  and  some  of  the  physical  constants  of  a 
few  members  of  this  series,  which  is  called  the  marsh  gas 
series  from  the  name  of  its  first  member,  or  the  paraffin 
series,  because  paraffin  includes  some  of  the  higher  mem- 
bers of  the  series. 

The  general  formula  for  the  marsh  gas  series  is  C^H^+g, 
in  which  n  stands  for  the  number  of  carbon  atoms  in  the 
molecule'.  .Thus  hexane  contains  6  carbon  atoms;  and 
twice  6,  plus  2,  or  14  hydrogen  atoms.  It  will  be  observed 
that  the  formula  of  each  member  differs  from  the  preced- 
ing by  CHa ;  such  a  series  is  called  a  homologous  series. 


476 


CLASSES   OF  CARBON  COMPOUNDS 


PARAFFIN   SERIES 


FORMULA 

MOLECULAR 
WEIGHT 

BOILING 
POINT 

FREEZING  (OR 

MELTING)  POINT 

Methane 

CH4 

16 

-  164°C 



| 

Ethane 

C2H8 

30 

-89.5 

— 

1  Ordinarily 

Propane 

C3H8 

44 

-38 

— 

|       gaseous 

Butane 

C4H10 

58 

+  1 

— 

J 

Pen  tan  e 
Hexane 

C6H12 
C6H14 

72 
86 

36 
71 

I 

>  Liquid 

Hexadecane 
Octodecane 

Ci6H34 
Ci8H38 

226 
254 

288 
317 

18° 
28 

}  Solid 

With  increasing  molecular  weight,  there  will  be  noticed 
a  rising  of  the  boiling  point  arid  the  tendency  to  assume 
the  solid  form  in  the  higher  members.  It  is  mixtures  of 
these  compounds  that  occur  in  petroleum  products. 

There  is  only  one  methane,  one  ethane,  and  one  propane, 
but  as  soon  as  we  reach  butane  it  is  possible  to  group  the 
atoms  in  more  than  one  way.  This  results  in  giving  two 
butanes,  CH3 — CH2 — CH2 — CH3,  normal  butane,  and 
CH 

CHo-J>CH,  isobutane,  both   of  which  are  known.     There 
CH/ 

are  4267  pentadecanes,  C15H32,  theoretically  possible. 

519.  Olefine  Series. — When  two  adjacent  carbon  atoms  are 
joined  by  a  double  bond,  a  new  series  of  hydrocarbons,  the 
olefine  or  ethylene  series,  results.  The  members  of  this  series 
have  the  general  formula  CnH2n.  Olefiant  gas,  a  valuable 
constituent  of  illuminating  gas,  is  the  simplest  member  of 

HH 

the  series.     Its  structural  formula  is 


ACETYLENE  477 

520.  Other  Series.  —  If  two  adjacent  carbon  atoms  are 
joined  by  a  triple  bond,  the  acetylene  series  results.  The 
general  formula  for  members  of  this  series  is  CnH2n_3. 
Acetylene,  H — C=C — H,  is  the  first  member  of  the 
series.  In  addition  to  the  hydrocarbons  already  men- 
tioned, many  other  series  exist.  Some  of  these  are  called 
ring  hydrocarbons  because  their  structural  formulas  show 
a  ring  formation.  Many  of  them  have  aromatic  odors 
and  give  the  series  the  name  aromatic.  Benzene,  derived 
from  coal  tar,  has  the  structural  formula : 

H 


/C\ 
TJO         ntr 
no         \JLL 

II      I 

HC        CH 


H 

This  is  the  starting  point  of  the  aromatic  series. 

521.  Methane,  or  Marsh  Gas.  —  Methane,  CH4,  is  a  col- 
orless, odorless  gas  which,  when  pure,  burns  with  a  non- 
luminous    flame.       It    is    often  formed    during    the    de- 
composition of  organic  matter,  as  in  swamps,  hence  its 
common  name,   marsh  gas.     It   is   the   principal  constit- 
uent  of   natural    gas.      In   soft    coal    mines,   the   miners 
call  it  fire  damp,  as   its   mixture   with   air   is   a   serious 
source  of  danger. 

522.  Acetylene.  —  Acetylene  has  been  mentioned  as  re- 
sulting from  the  reaction  of  calcium  carbide  and  water  : 

CaC2  +  2  H20  — >-  Ca(OH)2  +  C2H2 


478 


CLASSES   OF  CARBON   COMPOUNDS 


Ordinarily  it  burns  with  a 
smoky  flame,  but  with  a  suit- 
able burner  it  furnishes  a  bril- 
liant light  which  nearly  ap- 
proaches daylight  in  color 
value  (Fig.  149). 


FIG.   149.  —  ACETYLENE  FLAME. 
oil  that  boils  at  80°-85°. 


523.  Benzene.  —  Benzene,  or 
benzol,  C6H6,  is  a  light,  color- 
less, volatile  liquid,  having  a 
peculiar  odor.  Most  of  the 
benzol  is  obtained  from  the 
flue-gases  of  coke  ovens,  and 
from  coal  gas  during  its  puri- 
fication for  illuminating  pur- 
poses. It  is  also  obtained 
from  that  portion  of  coal  tar 
Benzene  burns  with  a  smoky 
flame.  It  is  a  good  solvent  for  resins  and  fats.  Its  prin- 
cipal use,  however,  is  for  the  production  of  more  complex 
compounds.  Unlike  the  paraffin  hydrocarbons,  the  coal 
hydrocarbons  react  with  comparative  ease,  as  with  nitric 
and  sulphuric  acid,  forming  important  compounds  used  in 
the  preparation  of  dyestuffs. 

524.  Substitution  Products  are  derived  from  hydrocarbons 
by  the  exchange  of  one  or  more  hydrogen  atoms  for  a 
corresponding  number  of  atoms  or  radicals.  The  chlorine 
substitution  products  of  methane  are  : 

CH3C1,  monochlormeih&ne. 

CH2C12,  dichlormeth&ne. 

CHC13,  trichlormQih&iie  (chloroform). 

CC14,  tetrachlormeth&ne  (carbon  tetrachloride). 


ALCOHOLS  479 

525.  Methyl  Chloride  is  a  gas  that   can   be  easily  com- 
pressed to  a  liquid,  and  is  sold  in  the  liquid  state  in  me- 
tallic cylinders.     It  is  used  as  a  local  anaesthetic,  produc- 
ing insensibility  by  freezing.     It  has  also  been  used  in  ice 
machines. 

526.  Chloroform.  —  Trichlormethane,  chloroform,  CHC13, 
is  a  heavy,  colorless,  easily  flowing  liquid.     It  has  a  pe- 
culiar odor  and  a  sweet  taste.     It  is  scarcely  soluble  in 
water.     Chloroform  is  a  most  valuable  anaesthetic  and  an 
important  solvent.     It  is  prepared  by  distilling  alcohol  or 
acetone  with  a  solution  of  bleaching  powder. 

527.  Carbon  Tetrachloride,  CC14,  is  prepared  in  the  pres- 
ence of  antimony  pentasulphide  by  passing  through  a  heated 
earthenware  tube  the  vapor  of  carbon  disulphide  mixed  with 
dry  chlorine.     It  is  a  low  boiling,  non-inflammable  liquid. 
It  is  used  as  a  solvent  for  grease  and  in  certain  types  of  fire 
extinguishers.     It  is  a  constituent  of  "Carbona." 

528.  Tri-iodomethane,  iodoform,  CHI3,  is  a  light  yellow 
powder  with  a  characteristic  odor.     It  is  useful  as  an  anti- 
septic.     Iodoform  may  be  prepared  by  the  reaction  of 
iodine  and  alcohol  rendered  slightly  alkaline. 

529.  Alcohols.  —  When  one   or   more  of  the  hydrogen 
atoms  of  a  hydrocarbon  are  substituted  by  a  correspond- 
ing  number   of  hydroxyl    (OH)    groups,    an   alcohol   is 
formed.     It  is  a  general  rule  that  two  hydroxyl  groups 
cannot  remain  attached  to  the  same  carbon  atom.     An 
alcohol  may  be  also  looked  upon  as  the  first  step  in  the 
oxidation  of  a  hydrocarbon.     Oxygen  enters  the  molecule 
between  an  atom  of  hydrogen  and  a  carbon  atom.     The 
alcohol   of   methane,    CH4,   is   methyl   alcohol,    CH3OH. 
The  alcohol  of  ethane,  C2H6,  is  ethyl  alcohol,  C2H5OH. 


480  CLASSES   OF  CARBON   COMPOUNDS 

Phenol  or  carbolic  acid,  C6H5OH,  is  an  alcohol  of  benzene, 
C6H6.  Glycerine  or  glycerol,  C3H6(OH)3,  is  an  alcohol  of 
propane,  C3H8.  In  this  case  each  carbon  atom  has  a  hy- 
droxyl  group  attached  to  it. 

530.  Methyl  Alcohol.  —  The  source  of  methyl  alcohol  is 
the   destructive   distillation    of   wood.       Impure   methyl 
alcohol  is  sold  as  wood  alcohol.     It  is  a  colorless  liquid  of 
low  boiling  point.     It  is  used  to  a  large  extent  as  a  sol- 
vent in  the  manufacture  of  varnishes.     Wood  alcohol  is  a 
very  convenient  fuel  where  small  quantities  of  heat  are 
required,  because  it  burns  with  a  clean  flame  of  high  heat 
value. 

531.  Ethyl  or  Grain  Alcohol.  —  This  is  ordinary  alcohol. 
The  only  important  source  of  ethyl  alcohol  is  the  fermen- 
tation of  certain  sugars  by  yeast.    Alcohol  is  obtained  from 
the  fermented  liquid  by  fractional  distillation.      Glucose, 
C6H12O6,  a  cheap  sugar  made  from  starch,  is  converted 
into  alcohol  and  carbon  dioxide  by  a  ferment  secreted  by 
the  yeast  plant : 

C6H1206  — >-  2  C2H6OH  +  2  CO2 

Ethyl  alcohol  resembles  methyl  alcohol  in  its  properties. 
It  is  a  low-boiling  liquid,  an  excellent  solvent  for  organic 
compounds,  and  it  burns  with  a  clean  flame  of  high  heat 
value.  As  a  constituent  of  alcoholic  beverages  it  is  manu- 
factured in  enormous  quantities.  These  beverages  owe 
their  intoxicating  properties  to  the  presence  of  alcohol. 

532.  Denatured  Alcohol.  —  Denatured   alcohol    is   ethyl 
alcohol  to  which  wood  alcohol  or  other  poisonous  sub- 
stances have  been  added  in  order  to  make  its  use  impossi- 
ble in  beverages  and  medicines.     In  countries  where  a 


ALDEHYDES  AND  KE TONES  481 

tax  is  imposed  on  alcoholic  liquors,  denatured  alcohol 
is  often  exempt,  so  that  the  cost  of  the  article  in  manu- 
facturing operations  shall  not  be  prohibitive.  Such  an 
exemption  law  is  in  force  in  this  country. 

In  the  United  States,  methyl  alcohol  and  benzene  are  two 
of  the  denaturing  agents  authorized  by  the  Commissioner 
of  Internal  Revenue.  The  proportions  by  volume  are  as 
follows : 

100  parts  ethyl  alcohol  (not  less  than  90  %  strength) 
10  parts  methyl  (wood)  alcohol 
J  part  benzene 

Such  alcohol  is  classed  as  completely  denatured,  but  there 
are  many  formulas  for  denaturization  to  suit  special  pur- 
poses. 

353.  Aldehydes  and  Ketones.  —  Three  classes  of  alcohols, 
primary,  secondary,  and  tertiary,  are  recognized  by  chem- 
ists. Primary  alcohols  have  their  hydroxyl  group  at- 
tached to  a  carbon  atom  bearing  2  hydrogen  atoms.  They 

f 

contain  the  group  — C — OH.      Secondary  alcohols  have 
H 

T 

the  general  formula  R — C — OH  in  which  R  may  stand  for 

R 

various  organic  radicals.  Their  hydroxyl  group  is  at- 
tached to  a  carbon  atom  combined  with  only  one  hydro- 
gen atom.  The  tertiary  alcohols  have  their  hydroxyl 
group  attached  to  a  carbon  atom  combined  with  these  or- 
ganic radicals  but  with  no  hydrogen. 


482  CLASSES  OF  CARBON  COMPOUNDS 

Aldehydes  result  from  the  oxidation  of  primary  alcohols. 
It  is  supposed  that  a  second  oxygen  atom  enters  the 
molecule  between  the  carbon  atom  carrying  the  hydroxyl 
group  and  one  of  the  hydrogen  atoms.  This  causes  two 
hydroxyl  groups  to  become  attached  to  the  same  carbon 
atom,  producing  an  unstable  compound,  according  to  the 
rule  stated  in  §  529.  A  molecule  of  water  separates 
from  the  unstable  compound  leaving  the  group  — C=O 

H 

which  is  the  distinguishing  characteristic  of  an  aldehyde. 
If  we  again  use  R  to  represent  an  organic  radical,  the 
changes  may  be  represented  as  follows : 

H  OH 

R__C_OH  +  O  — >-  R—C— OH  — >-  H2O  +  R— C=O 
H  H  H 

alcohol  unstable  aldehyde 

compound 

During  the  process  the  alcohol  loses  two  atoms  of  hydro- 
gen and  this  gave  the  product  the  name  aldehyde,  that  is, 
dehydrogenated  alcohol. 

Similar  changes  take  place  on  the  oxidation  of  second- 
ary alcohols,  and  bodies  called  Jcetones  result.  A  ketone 
is  a  compound  corresponding  to  the  general  formula 
R— C=O. 


534.  Formaldehyde  is  prepared  by  the  slow  oxidation  of 
methyl  alcohol.  It  has  the  formula  H— C=O.  Formal- 
dehyde is  a  very  valuable  disinfectant  and  preservative. 


ACETIC  ACID  483 

It  is  a  gas  at  ordinary  temperatures,  but  it  comes  into  the 
market  as  a  water  solution  known  as  formalin. 


535.    Acetone,    C=O,    is    a    ketone    derived    from   the 

CH3 

products  obtained  by  the  destructive  distillation  of  wood. 
Acetone  is  a  colorless  liquid  possessing  a  characteristic 
odor.  It  is  extensively  used  as  a  solvent  for  resins  and 
gums,  and  in  the  manufacture  of  chloroform.  It  is  an  ex- 
cellent solvent  for  acetylene.  Prest-O-Lite  cylinders  are 
filled  with  asbestos  that  has  been  soaked  in  acetone. 
Acetylene  under  pressure  is  then  dissolved  in  the  acetone. 
When  the  pressure  is  removed  by  opening  the  valve  of 
the  tank,  the  acetylene  passes  out  of  solution  and  escapes. 

ACIDS 

When  aldehydes  are  oxidized,  acids  result. 
R— C= 


-C=O  +  O  — >-  R— C=O 
H  OH 


The  group  — C=O,  called  the  carboxyl  group,  is  charac- 

OH 

teristic  of  organic  acids.  The  hydrogen  of  the  carboxyl 
group  is  the  hydrogen  of  the  acid  that  can  be  replaced  by 
a  metal.  A  number  of  organic  acids  are  common  useful 
substances. 

536.   Acetic  Acid,   CH3— C=O  or   H(C2H3O2-),  is   the 

6H 

acid  contained  in  vinegar.  It  is  obtained  from  the  de- 
structive distillation  of  wood,  and  is  produced  by  the 


484  CLASSES  OF  CARBON  COMPOUNDS 

action  of  the  acetic  acid  ferment  (mother  of  vinegar)  on 
impure  dilute  solutions  of  alcohol.  The  sugar  of  apple 
cider  is  changed  to  carbon  dioxide  and  alcohol  by  a  fer- 
ment of  the  yeast  plant  : 


Then  the  acetic  acid  ferment  converts  the  alcohol  into 
vinegar  : 

C2H5OH  +  02  —  ^  H20  +  H(C2H302) 

Glacial  acetic  acid  contains  less  than  1  %  of  water  ;  com- 
mercial acetic  acid  contains  about  30  %  of  the  anhydrous 
acid.  Acetic  acid  is  used  in  the  manufacture  of  white  lead, 
as  a  solvent  for  various  organic  substances,  and  in  the 
manufacture  of  the  coal  tar  colors. 

537.  Oxalic  Acid,  COOH  or  H2C2O4,  is  obtained  by  heat- 

COOH 

ing  sawdust  in  the  presence  of  caustic  soda,  neutralizing 
a  water  solution  of  the  product  with  calcium  hydroxide, 
and  then  decomposing  the  calcium  oxalate  with  sulphuric 
acid.  Commercial  oxalic  acid  contains  water  of  crystal- 
lization as  shown  by  the  formula  H2C2O4  •  2  H2O.  Sub- 
limed oxalic  acid  is  anhydrous.  Oxalic  acid  is  a  mild 
reducing  agent  and,  on  this  account,  is  frequently  used 
in  the  removal  of  iron  rust  and  ink  spots  from  white  cloth, 
and  for  bleaching  straw  hats.  It  is  also  used  for  clean- 
ing copper  and  brass.  Oxalic  acid  is  an  important  re- 
agent in  analytical  laboratories  and  is  used  in  calico 
printing,  dyeing,  and  tanning. 

The  fact  that  oxalic  acid  is  a  poison  should  not  be  for- 
gotten when  the  acid  is  kept  in  the  house. 

538.  Important  Fruit  Acids.  —  Tartaric  Acid,  H3(C4H4O6), 
is  made  from  crude  cream  of  tartar  which  deposits  on  the 


NITROGLYCERIN  485 

side  walls  of  wine  vats  during  the  fermentation  of  grape 
juice.  Potassium  acid  tartrate,  KH(C4H4O6),  is  cream  of 
tartar. 

Citric  Acid,  H3(C6H5O7),  is  found  in  the  juices  of 
lemons,  oranges,  limes,  gooseberries,  and  several  other 
kinds  of  fruit. 

ESTERS,   OR  ETHEREAL  SALTS 

539.  Formation   and   Uses.  —  An   ester  and   water  are 
formed  by  the  action  of  an  acid  with  an  alcohol.     The  re- 
action is  analogous  to  that  which  takes  place  during  the 
formation  of  a  salt  by  neutralization.     The  alcohol  may 
therefore  be  considered  as  taking  the  part  of  a  base : 

NaOH  +  H(C2H8O2)  — >-  H2O  +  Na(C2H3O2) 

sodium  acetate 

C2H6OH  +  H(C2H302)  — ^H20  +  C2H6(C2H3Oa) 

ethyl  acetate 

The  esters  form  an  important  group  of  compounds. 
Some  are  employed  in  medicine,  while  others  are  used  in 
the  preparation  of  perfumery.  Many  are  used  in  making 
artificial  fruit  flavors.  The  characteristic  flavor  of  the 
pineapple  is  due  chiefly  to  ethyl  butyrate ;  oil  of  winter- 
green  is  methyl  salicylate. 

540.  Nitroglycerin. —Nitroglycerin,  C3H5(NO8)3,  is  an 
ester  of  an  alcohol  (glycerin)  and  nitric  acid.     It  is  pre- 
pared by  the  action  of  glycerin,   C3H5(OH)3,  with  a  mix- 
ture of  concentrated  nitric  and  sulphuric  acids: 

C8H8(OH)8  +  3  HN03— s-  3  H2O  +  C8H5(NO8)8 

The  sulphuric  acid  aids  the  action  by  uniting  with  the 
water  formed  during  the  reaction.  The  concentration  of 
the  free  nitric  acid  is  thus  kept  at  maximum.  Nitro- 


486  CLASSES   OF  CARBON  COMPOUNDS 

glycerin  is  a  highly  explosive  liquid  at  ordinary  tem- 
peratures. Dynamite  is  nitroglycerin  which  has  been 
absorbed  by  infusorial  earth,  or  by  a  mixture  of  wood  pulp 
and  sodium  nitrate. 

541.  Oils,  Fats,  and  Soaps.  —  Oils  and  fats  are  esters  of 
glycerine  and  various  fatty  acids.     The  chief  constituent 
of  beef  tallow  is  glyceryl  stearate,  an  ester  of  glycerine 
and  stearic  acid,  commonly  called  stearin.     It  is  formed 
by   the  reaction  between  one  molecule  of  glycerine  and 
three  molecules  of  stearic  acid. 

When  such  a  fat  is  boiled  with  a  solution  of  sodium 
hydroxide,  a  molecule  of  glycerine  and  three  molecules  of 
sodium  stearate,  a  hard  soap,  results  from  the  reaction : 

C3H5(C18H3602)3   +      3NaOH   -  -^  C3H5(OH)3  +  3  NaC18H3502 

glyceryl  stearate  sodium  hydroxide  glycerine  sodium  stearate 

Common  hard  soap  is  a  mixture  of  sodium  salts  of  fatty 
acids,  chiefly  stearic,  palmitic,  and  oleic  acids.  Soft  soap 
is  generally  a  mixture  of  the  potassium  salts  of  the  fatty 
acids.  The  term  soap  is  applied  in  general  to  any  me- 
tallic salt  of  a  fatty  acid. 

Sodium  and  potassium  soaps  are  soluble  in  water. 
Soaps  of  the  other  common  metals  are  insoluble. 

542.  Hard  Water  and  Soap.  —  When  a  soluble  soap,  for 
example  sodium  stearate,  is  used  with  a  water  containing 
calcium  ions,  an  insoluble  calcium  soap,  calcium  stearate, 
is  formed : 

2  Na(C18H3502)  +  CaS04  — >-  Ca(C18H35O2)2  +  Na2SO4 

The  soap  is  said  to  be  destroyed,  as  good  suds  cannot 
be  formed  until  the  calcium  ions  are  removed  from 
solution.  This  explains  why  hard  water  is  not  desirable 


STARCH  487 

for  washing  purposes.  The  hardness  of  water  is  measured 
by  its  soap-destroying  power.  This  is  commonly  due  to 
the  presence  of  calcium  and  magnesium  ions  in  the  water. 
Soap  does  not  form  suds  with  salt  water  because  it  does 
not  go  into  solution.  Salt  water  contains  a  large  number 
of  sodium  ions  and  these  keep  the  soap  from  dissolving. 

543.  Ether.  —  Ordinary  ether,  C4H10O,  may  be  regarded 
as  ethyl  oxide,  (C2H5)2O.  It  is  prepared  by  treating 
alcohol  with  a  dehydrating  agent,  such  as  sulphuric  acid : 

2  C2H6OH  _».  (C2H6)20  +  H20 

Ether  is  a  volatile,  inflammable  liquid,  boiling  at  35°C. 
It  is  used  as  a  solvent  and  as  an  anaesthetic. 


CARBOHYDRATES 

The  carbohydrates  are  chemical  compounds  composed 
of  carbon  united  to  hydrogen  and  oxygen,  the  last  two 
elements  being  in  the  same  proportion  as  in  water.  Starch, 
cellulose,  glucose,  and  sugar  are  common  carbohydrates. 

544.  Starch,  (C6H10O5)n,  is  formed  in  the  leaves  of 
plants  by  the  action  of  chlorophyll  and  sunlight  on  carbon 
dioxide  and  water : 

6  C02  +  5  H20  — ^  C6H1005  +  6  O2 

From  the  leaves,  it  is  carried  to  other  parts  of  the  plant 
and  is  often  stored  in  roots,  tubers,  and  seeds.  Starch 
reacts  with  dilute  solutions  of  iodine.  The  product  has  a 
beautiful  blue  color.  This  reaction  is  used  as  a  test  for 
either  iodine  or  starch. 

Dilute  acids  convert  starch  into  glucose,  and  much 
starch  is  used  for  this  purpose.  Dextrin  is  prepared  by 


488  CLASSES   OF  CARBON  COMPOUNDS 

heating  dry  starch  to  about  250°  C.  It  is  a  valuable 
constituent  of  food,  and  is  the  adhesive  used  on  the  back 
of  postage  stamps. 

Sprouting  barley  contains  ^an  enzyme  (ferment)  known 
as  diastase,  which  is  capable  of  converting  starch  into  a 
sugar  named  maltose.  In  the  manufacture  of  malt,  the 
grain  is  allowed  to  germinate  to  produce  the  enzyme,  after 
which  the  process  is  stopped  by  heating  the  barley  to  60°. 
At  a  temperature  of  about  70°  C.,  the  diastase  rapidly  con- 
verts the  starch  which  the  grain  contains  into  maltose  and 
dextrose. 

545.  Cellulose.  —  The  cell  walls  of  plants  are  composed 
of  cellulose,  a  compound  having  a  percentage  composition 
corresponding  to  the  formula  C6H10O5.  Absorbent  cot- 
ton and  the  better  grades  of  filter  paper  are  pure  cellulose. 
It  is  the  chief  constituent  of  straw  and  wood. 

When  boiled  with  acids,  cellulose  is  slowly  converted 
into  a  sugar  called  glucose.  Cellulose  dissolves  without 
change  in  an  ammoniacal  solution  of  cupric  hydroxide, 
known  as  Schweitzer's  reagent.  The  cellulose  can  be 
precipitated  from  such  a  solution  by  the  addition  of  alcohol. 
Concentrated  solutions  of  sodium  hydroxide  convert  cel- 
lulose into  soda  cellulose.  This,  when  treated  ^ith  car- 
bon disulphide,  yields  viscose,  a  substance  readily  soluble 
in  water.  Cuprammonium  solutions  of  cellulose  and  also 
viscose  are  used  in  the  manufacture  of  artificial  silks, 
which,  since  the  finished  product  consists  of  cellulose, 
are  more  properly  called  luster  celluloses.  Cellulose  is 
dissolved  in  zinc  chloride  in  making  the  filaments  for  in- 
candescent electric  light  bulbs.  Acetic  anhydride  is  used 
to  convert  cellulose  into  cellulose  acetate,  a  substance 
useful  in  the  manufacture  of  electric  insulators  and  mov- 
ing picture  films. 


SUGARS  489 

546.  Nitroeelluloses.  —  If   the    formula  for    cellulose   is 
considered  to  be  (C6H10O6x)2,  from  two  to  six  nitro  (NO2) 
groups  can  be  introduced  into  the  molecule.     Thus,  when 
pure  cotton  fiber  is  treated  with  a  mixture  of  nitric  and 
sulphuric  acids,  products  are  obtained  which  may  contain 
two,  three,  four,  five,  or  six  nitro  groups ;  the  number  de- 
pends upon  the  concentration  of  the  acids  and  the  time 
during  which  they  are  allowed  to  act. 

The  di-,  tri-,  tetra-,  and  penta-nitrocelluloses  are  known 
as  soluble  guncotton.  Hexanitrocellulose  is  insoluble  gun- 
cotton.  Collodion  is  a  solution  of  soluble  guncotton  in  a 
mixture  of  alcohol  and  ether.  Such  a  solution  is  used  as 
liquid  court  plaster.  Celluloid  is  made  by  dissolving  the 
lower  nitrates  of  cellulose  in  camphor  and  then,  by  heat 
and  pressure,  working  the  mass  into  the  desired  shape. 
Explosive  gelatine  consists  of  guncotton  dissolved  in  nitro- 
glycerin. 

547.  Sugars.  —  A   very   large    number   of    sugars   are 
known.     Fructose,  or  fruit  sugar ;  glucose,  or  grape  sugar ; 
and  saccharose,  or  cane  sugar,  —  are  among  the  more  impor- 
tant.    Fructose  and  glucose  have  the  empirical  formula 
C6H12O6 ;  the  formula  for  saccharose  is  Gl2H^Olr 

Glucose  is  converted  by  a  ferment  (zymase)  secreted 
by  the  yeast  plant  into  alcohol  and  carbon  dioxide : 

C6Hi2°6  +  zymase— »-  2  C2H5OH  +  2  CO2 

This  fermentation  is  made  use  of  in  the  raising  of  bread 
and  in  the  preparation  of  alcohol.  It  also  is  the  cause  of 
the  formation  of  hard  cider. 

The  manufacture  of  glucose  from  starch  has  already 
been  referred  to.  Large  quantities  of  glucose  are  used  in 
making  candies  and  table  syrups.  Common  sugar,  saccha- 
rose, is  obtained  from  the  sap  of  the  sugar  cane,  sugar  beet, 


490 


CLASSES   OF  CARBON  COMPOUNDS 


and  sorghum.      It   is   also  -the  principal   constituent   of 
maple  sugar  (Fig.  150). 


'Fie.  150.  —  COLLECTING  SAP  FOR  MAPLE  SUGAR. 

Saccharose  is  converted  into  glucose  and  fructose  by 
boiling : 

C12H22(D11  +  H2<D  — *-  C6H12<})6  +  C6H12d>6 

Glucose  and  fructose  have  the  same  empirical  formula. 

Dilute  acids  hasten  this  action,  which  is  known  as  inver- 
sion. For  this  reason  vinegar  is  often  added  to  sugar 
during  the  making  of  candy  that  is  to  be  pulled. 

Zymase  does  not  convert  saccharose  into  alcohol  and 
carbon  dioxide.  However,  the  yeast  plant  secretes  an- 
other ferment  called  invertase  which  changes  saccharose 


SUMMARY  491 

to  a  mixture  of  glucose  and  fructose.     These,  as  has  al- 
ready been  mentioned,  can  be  fermented  by  zymase. 

Common  sugar  melts  at  160°  C.  to  a  colorless  liquid 
which  solidifies  on  sudden  cooling  to  a  transparent  amber- 
colored  mass,  called  barley  sugar.  When  sugar  is  heated 
to  215° C.,  some  water  is  expelled  and  a  brown  mass,  car- 
amel, is  obtained. 

SUMMARY 

A  structural  formula  is  used  to  represent  the  arrangement  of 
the  atoms  composing  a  molecule.  On  account  of  the  large  num- 
ber of  carbon  compounds  that  have  the  same  empirical  formula, 
it  is  generally  desirable  to  use  a  structural  formula  to  represent 
graphically. the  chemical  nature  of  a  carbon  compound. 

A  hydrocarbon  is  a  compound  composed  of  hydrogen  and  carbon 
only.  The  hydrocarbons  of  the  methane  series  have  the  general 
formula  CnH2w+2;  those  of  the  olefiant  series,  CrtH2n;  those  of 
the  acetylene  series,  CnH  2n_2 ;  and  those  of  the  benzol  series, 
CnH2n_6.  In  these  formulas  n  stands  for  the  number  of  carbon 
atoms.  Marsh  gas,  acetylene,  and  benzol  are  important  hydro- 
carbons. 

Substitution  products  are  formed  when  one  or  more  of  the 
hydrogen  atoms  of  a  hydrocarbon  are  exchanged  for  an  equiva- 
lent number  of  atoms  of  some  other  element,  generally  a  halogen, 
or  an  equivalent  number  of  radicals.  Chloroform,  iodoform, 
and  carbon  tetrachloride  are  common  substitution  products. 

Alcohols  may  be  considered  as  derived  from  hydrocarbons  by 
substituting  one  or  more  hydroxyl  groups  for  a  corresponding 
number  of  hydrogen  atoms.  As  a  rule,  two  hydroxyl  groups 
cannot  remain  attached  to  the  same  carbon  atom.  Methyl 
alcohol,  ethyl  alcohol,  and  glycerine  are  important  alcohols. 

Denatured  alcohol  is  ethyl  alcohol  to  which  substances,  gener- 
ally methyl  alcohol  and  benzene,  have  been  added  to  make  it  un- 
fit for  use  in  beverages  and  in  medicines. 


492  CLASSES   OF  CARBON  COMPOUNDS 

Aldehydes  contain  the-  group  — C=O.      Formaldehyde  is  the 

H 
most  common  aldehyde. 

Ketones  have   the   general    formula    R — C=O,  in  which  R 

R 

stands  for  an  organic  radical.     Acetone  is  an  important  ketone. 
Organic  acids    contain   the    carboxyl   group  — C=0.     Acetic 

OH 
acid,  oxalic  acid,  and  tartaric  acid  are  familiar  organic  acids. 

Esters  or  ethereal  salts  and  water  result  from  the  reaction  be- 
tween acids  and  alcohols,  the  alcohol  playing  the  part  of  a  base. 
Sulphuric  acid  is  generally  used  to  aid  the  reaction.  Nitro- 
glycerin  and  animal  and  vegetable  fats  are  esters. 

A  soap  is  a  metallic  salt  of  a  fatty  acid.  Sodium  and  potas- 
sium soaps  are  soluble  in  water.  Soaps  of  other  common 
metals  are  insoluble. 

A  water  is  said  to  be  hard  when  it  contains  some  substance 
that  will  react  with  washing- soap  to  yield  an  insoluble  soap. 

Ether  is  ethyl  oxide,  (C2H6)2O. 

Carbohydrates  are  compounds  containing  carbon  in  combina- 
tion with  hydrogen  and  oxygen ;  they  always  contain  two  atoms 
of  hydrogen  for  each  atom  of  oxygen  in  the  molecule.  Starch, 
cellulose,  glucose,  and  sugar  are  common  hydrocarbons. 


EXERCISES 

1.  Why  is   it   frequently   desirable   to   use   the   structural 
formula  of  an  organic  compound  ? 

2.  What  is  a  hydrocarbon  ? 

3.  A   hydrocarbon   of  the   methane   series   contains   three 
carbon  atoms.     Give  its  structural  formula. 


EXERCISES  493 


4.  How  many  pentanes  (CgH^)  are  possible  ?    Write  their 
structural  formulas. 

5.  What  is  the  structural  formula  for  acetylene  ? 

6.  Why  is  carbon  tetrachloride  preferable  to  gasoline  for 
the  removal  of  grease  spots  from  clothing  in  the  home  ? 

7.  Define  alcoholic  fermentation  ;  acetic  fermentation. 

8.  What  is  an  alcohol  ? 

9.  Give  the  formulas  for  three  common  alcohols. 

10.  What  is  denatured  alcohol  ?     Why  is  alcohol  denatured  ? 

11.  What  group  of  elements  is  characteristic  of  aldehydes  ? 

12.  What  relation  does  formaldehyde  bear  to  wood  alcohol  ? 

13.  To  what  class  of  organic  compounds  does  acetone  belong  ? 

14.  What  is  Prest-O-Lite  ? 

15.  What  group  of   elements   is   characteristic   of  organic 
acids? 

16.  What  relation  does  acetic  acid  bear  to  alcohol  ? 

17.  To  what  class  of  compounds  do  animal  and  vegetable 
fats  belong  ? 

18.  What  is  nitroglycerin  ?     Dynamite  ? 

19.  What  reaction  takes  place  when  soap  is  added  to  a  water 
containing  magnesium  sulphate  ?     Why  ? 

20.  Why  do  not  soap  suds  form  readily  when  soap  is  added 
to  salt  water  ? 

21.  Name  three  common  carbohydrates. 

22.  How  may  alcohol  be  obtained  from  glucose  ?     Equation. 

23.  Name  a  solvent  for  cellulose. 

24.  How  is  dextrin  obtained  from  starch  ? 

25.  Would  you  expect  to  find  dextrin  in  the  crust  or  in  the 
center  of  a  loaf  of  bread  ? 

26.  Why  is  vinegar  used  in  making  sugar  candy  that  is  to 
be  pulled? 

27.  What  is  barley  sugar  ?     Caramel  ? 


CHAPTER   XL 
RADIUM  AND  RADIOACTIVITY 

548.  The    Discovery    of    Radioactivity.  —  In    1896    the 
French  chemist  Becquerel,  while  investigating  the  pene- 
trating powers  of  the  rays  emitted  by  phosporescent  sub- 
stances, happened  to  leave  a  compound  of  the  element 
uranium  spread  out  on  the  thick  paper  that  inclosed  a 
photographic  plate.     At  the  end  of  four  weeks  it  was 
found  that  the  plate  had  been  affected  by  rays  which  had 
issued  from  the  uranium  compound,  and  which  had  pene- 
trated the  thick  paper  that  inclosed  the  plate.     Investiga- 
tion showed  that  the  result  was  in  no  way  connected  with 
the    phosphorescent   properties    of    the    substance,    since 
identical  effects  were  observed  whether  the  uranium  com- 
pound was  in  the  phosphorescent  state  or  not.     It  ap- 
peared that  the  substance  continuously  gave  off  rays  which 
produced  photographic  and  electrical  effects  without  being 
itself  changed  in  the  process. 

This  half -accidental  discovery  of  Becquerel's  led  to  in- 
vestigations which  have  marked  an  important  era  in  the 
history  of  chemistry.  The  term  radioactivity  was  given 
to  effects  like  those  produced  by  uranium  compounds. 

549.  The  Discovery  of  Radium.  —  Madame  Curie,  a  Pol- 
ish woman  resident  in  Paris,  took  up  a  series  of  researches 
along  the  line  indicated  by  Becquerel's  discovery.     She 
found  that  all  uranium  compounds  possess  radioactivity, 
and  hence  that  this  is  a  property  of  the  uranium  atom. 

494 


Marie  Slodowska  Curie  was  born  in  Warsaw,  Poland,  in  1867. 
Her  work  began  with  the  investigation  of  radio-activity  first 
noticed  by  Becquerel  in  connection  with  uranium.  She  first  iso- 
lated polonium,  an  element  possessed  of  radio-activity  in  high 
degree,  and  later,  in  collaboration  with  her  husband,  Pierre  Curie, 
made  the  epoch-making  discovery  of  radium.  For  this  work  they 
received  the  Davy  Medal  of  the  British  Royal  Society,  and  shared 
with  Becquerel,  in  1903,  the  award  of  the  Nobel  Prize  in  Physics. 
Madame  Curie  succeeded  her  husband  as  the  holder  of  one  of  the 
most  important  chairs  of  science  in  the  world,  the  Professorship 
of  Physics  at  the  Sorbonne,  University  of  Paris. 


THE  NATURE   OF  RADIOACTIVITY  495 

She  then  observed  that  pitchblende,  the  mineral  from 
which  uranium  is  usually  obtained,  is  more  radioactive 
than  might  be  expected  from  the  amount  of  uranium 
present.  She  reasoned  that  the  mineral  must,  therefore, 
contain  something  more  active  than  uranium.  Working 
with  this  point  in  view,  she  found  that  bismuth  and  barium 
when  extracted  from  pitchblende  are  radioactive.  But 
ordinary  bismuth  and  barium  are  not  radioactive.  Hence 
it  was  probable  that  when  extracted  from  pitchblende  the 
two  metals  contained  small  quantities  of  other  elements, 
chemically  similar  themselves,  and  radioactive  in  a  high 
degree.  Madame  Curie  set  out  to  find  these  elements. 

She  was  soon  able  to  show  that  bismuth  obtained  from 
pitchblende  is  in  reality  associated  with  an  element  many 
times  more  active  than  uranium.  This  element  was 
named  polonium  in  honor  of  her  native  country. 

Her  next  work,  done  in  collaboration  with  M.  Curie, 
resulted  in  what  probably  always  will  be  regarded  as  one 
of  the  greatest  of  chemical  discoveries.  This  was  the 
separation  of  a  minute  quantity  of  the  element  that  is  as- 
sociated with  pitchblende  barium.  It  was  named  radium 
because  of  the  extraordinary  degree  of  radioactivity  that 
it  exhibited.  The  study  of  this  remarkable  substance  has 
led  to  a  better  understanding  of  the  nature  of  atoms,  and 
to  important  changes  in  chemical  theories. 

550.  The  Nature  of  Radioactivity.  —  The  peculiar  char- 
acteristics possessed  by  radioactive  bodies  are  due  to 
emanations  or  radiations  that  they  produce  without 
undergoing  any  apparent  change.  Three  types  of  such 
emissions  have  been  recognized.  They  are  designated  by 
three  Greek  letters,  a  (alpha),  ft  (beta),  and  7  (gamma). 
The  first  of  these,  the  a  emanation,  has  played  the  most 
important  part  in  radium  investigations.  The  basis  of  the 


496  RADIUM  AND  RADIOACTIVITY 

classification  of  the  three  types  of  rays  was  their  penetrat- 
ing power.  The  a  type  has  the  least  power,  though  these 
rays  will  pass  through  a  sheet  of  paper  or  even  through 
very  thin  glass.  The  0  rays  have,  roughly  speaking,  100 
times  the  penetrating  power  of  the  a  type,  and  the  7  rays 
have  about  10,000  times  the  power  of  the  a.  These  7  rays 
will  traverse  a  foot  of  solid  iron  or  six  inches  of  the  dense 
metal  lead.  They  are  identical  with  X-rays  discovered 
by  Roentgen.  The  /3  rays  consist  of  minute  particles  of 
negative  electricity  (electrons). 

The  a  radiation  has  been  shown  to  be  atoms  of  the  ele- 
ment helium  positively  electrified.  Helium  has  been  recog- 
nized as  an  element  for  many  years.  It  was  first  discovered 
by  the  aid  of  the  spectroscope  as  a  constituent  of  the 
gases  that  surround  the  sun.  A  few  years  before  the 
radium  investigations  it  was  found  as  one  of  the  rare 
gases  of  the  atmosphere.  Thus  through  radium  we  have 
found  an  actual  case  of  the  transmutation  of  elements, 
and,  in  a  sense,  the  old,  laughed-at  idea  of  the  alchemists 
has  been  revived  in  the  mind  of  chemists. 

Another  extraordinary  thing  about  radium  is  that  it  is 
continually  giving  off  energy  through  its  emanations. 
When  a  bit  of  radium  is  placed  beside  the  bulb  of  a  ther- 
mometer and  the  two  are  wrapped  in  a  bit  of  cotton  or 
wool,  the  thermometer  stands  a  degree  or  two  higher  than 
the  temperature  of  the  room.  But  so  far  as  ordinary  ob- 
servation reveals,  the  substance  is  absolutely  unchanged 
either  in  properties  or  weight.  Here  we  have  an  apparent 
contradiction  of  the  law  of  the  conservation  of  energy. 
Another  and  more  striking  experiment  showing  the  continu- 
ous emission  of  energy  is  found  in  the  radium  clock  (Fig. 
151).  A  small  quantity  of  radium  bromide  is  contained 
in  a  metal  tube  from  which  are  suspended  two  pieces  of 
gold  leaf.  The  leaves  separate  owing  to  the  fact  that 


RADIOACTIVE  DECAY 


497 


they  are  electrically  charged  by  the  effect  of  the  radium. 
On  diverging,  the  leaves  touch  the  strips  of  metal  on  the 
inside  of  the  bottle  which  contains  the  apparatus  and  dis- 
charge their  electricity.  They  then  fall  together,  are 
again  charged  by  the  radium,  and  again 
separate.  Since  the  radium  compound  does 
not  apparently  diminish  in  producing  this 
action,  the  clock  will  seemingly  go  on  for- 
ever. In  other  words,  we  have  realized  a 
sort  of  perpetual  motion. 

These  three  examples  will  serve  to  show 
how  radium  seemed  to  upset  established 
physical  and  chemical  ideas.  It  remains 
for  us  to  show  how  these  things  were  rec- 
onciled with  the  older  knowledge. 

551.  Radioactive  Decay.  —  Let  us  consider 
further  experimental  facts.  Radium  is 
always  found  in  ores  that  contain  uranium, 
in  the  definite  proportion  of  1  part  of 

radium  for  about   3,200,000   parts  of  ura-       FIG.  151. 

nium.  Radium  compounds  when  recrystal-  RADIUM  CLOCK. 
lized  from  water  solution  are  found  to 
be  inactive,  but  regain  their  activity  on  standing  a  few 
days.  The  water  which  was  used  in  the  process  gives 
off  a  minute  quantity  of  a  gas,  that,  mixed  with  air, 
can  be  aspirated  from  one  vessel  to  another,  and  that 
rapidly  loses  its  activity,  so  that  in  a  little  over  five 
days  it  is  only  half  as  active  as  before.  Objects  that 
come  in  contact  with  this  gas,  or  that  have  been  near 
radium,  become  active  ;  but  if  these  objects  are  rubbed 
with  sandpaper,  the  activity  is  found  to  be  attached  to 
the  scraping  material ;  this  acquired  activity,  however, 
decays  to  half  its  value  in  about  thirty  minutes. 


498  RADIUM  AND  RADIOACTIVITY 

These  facts  have  been  studied  .and  satisfactory  and  con- 
sistent explanations  have  been  found  for  the  whole  range 
of  observations.  This  has  been  done  by  the  aid  of  instru- 
ments so  sensitive  that  quantities  of  radioactive  materials 
can  now  be  recognized  that  would  be  a  million  times  too 
small  to  be  detected  by  the  older  methods. 

552.  Radioactive   Series.  —  In   adopting  these   new  ex- 
planations it  was  found  necessary  to  abandon  the  old  idea 
that  an  atom  is  an  unchangeable  thing.     It  is  now  believed 
that    radioactive   elements  are   continuously   undergoing 
processes   of   decomposition.     During   the    changes,    two 
important  things  occur :   (a)  relatively  enormous  amounts 
of  energy  are  liberated,  and  (6)  new  elements  are  produced. 
It  appears  that  certain  of  the  atoms  explode  from  time  to 
time,  producing  the  various  radioactive  effects.     Helium 
atoms  result  in  many  cases,  and  sometimes  /3  and  7  radia- 
tions.    In   each  case,  the  greater  part  of  the  exploding 
atom  remains  intact  and  forms  the  atom  of  a  new  element. 
This  explodes  in  its  turn,  and  thus  we  have  a  series  of 
radioactive  elements  resulting  from  one  parent  element. 
During  the  transformations,  the  atomic  weights  continually 
decrease.     A   helium   atom    weighs   4,  and  when  one  of 
these   is   evolved,  we   find    that  the   atom   which  is  left 
weighs  4  less  than  its  parent  atom. 

Two  main  series  of  such  radioactive  transformation 
have  been  recognized.  Uranium  is  the  parent  element  in 
one  series,  and  thorium  in  the  other. 

553.  The   Uranium   Series.  —  Different   radioactive   ele- 
ments vary  greatly  in  the  speeds  with  which  they  decom- 
pose.    The  less  active  ones  decompose  slowly,  the  more 
active  rapidly.     Thus,  in  the  case  of  uranium,  which  is 
very  slightly  active,  it  has  been  calculated  that  it  would 


DECOMPOSITION  OF  ATOMS  499 

take  8,000,000,000  years  for  half  of  the  atoms  in  a  given 
mass  to  change  into  other  substances.  It  would  take 
another  8,000,000,000  years  for  half  of  the  remainder  to 
decompose,  and  so  on.  The  "  life  "  or  period  of  one  of 
these  elements  is  measured  by  the  time  it  would  take  for 
half  of  its  atoms  to  change. 

The  uranium  atom,  atomic  weight  238,  in  decomposing, 
produces  an  atom  of  helium,  atomic  weight  4,  and  an  atom 
of  uranium  II,  atomic  weight  234,  period  2,000,000  years. 
The  transformation  goes  on  through  two  other  elements, 
uranium  X,  period  35.5  days,  and  ionium,  period  200,000 
years,  to  radium,  atomic  weight  226.  This  element  has 
played  the  most  important  part  in  radioactive  investiga- 
tions because  its  period,  which  is  2500  years,  is  long  enough 
to  permit  study,  and  at  the  same  time  short  enough  to 
give  to  the  element  a  high  degree  of  radioactivity. 

'  Radium  atoms  in  their  explosions  give  off  helium  atoms 
and  a  new  element  described  above  as  the  gas  obtained 
from  solutions  of  radium  salts.  This  is  an  extremely 
active  substance  whose  period  is  5.6  days.  Its  atomic 
weight  is  222,  and  it  has  been  identified  by  Ramsay  as 
niton.  The  decompositions  continue  from  this  element 
through  several  others  of  extremely  short  period,  ending 
with  polonium,  with  a  period  of  202  days,  and  an  atomic 
weight  of  210.  Some  of  these  short-lived  elements  con- 
stitute the  deposit  found  on  substances  that  have  been 
near  radium  salts.  This,  by  loss  of  a  helium  atom,  becomes 
an  element  of  atomic  weight  206.  This  is  the  value  for 
lead  and  it  is  believed  that  this  element  is  the  final  result 
of  the  series  of  uranium  decompositions. 

554.  The  Thorium  Series.  —  Thorium  is  a  comparatively 
rare  element  whose  oxide  has  become  commercially  im- 
portant in  recent  years  as  the  chief  constituent  of  gas 


500  RADIUM  AND  RADIOACTIVITY 

mantles.  It  is  a  radioactive  substance  of  long  period, 
probably  25,000,000,000  years.  As  we  would  expect  from 
this  figure,  it  is  not  a  very  active  substance.  But  there 
are  always  found  associated  with  the  natural  deposit  of  the 
thorium  mineral  small  quantities  of  its  decomposition 
products,  and  some  of  these  are  more  active  than  radium. 
They  are  separated  with  the  by-products  during  the  process 
of  purification,  and  we  have  thus  an  important  source  of 
radioactive  material. 

Thorium  itself  slowly  produces  mesothorium  I  with  loss 
of  a  helium  atom.  This  element  is  interesting  because  it 
is  chemically  identical  with  radium,  and  can  only  be  dis- 
tinguished from  radium  by  the  difference  in  its  period, 
that  of  mesothorium  being  7.9  years.  It  is  an  intensely 
active  substance,  which  makes  a  good  substitute  for 
radium  in  studying  radioactivity.  Some  eight  or  nine 
other  elements  have  been  recognized  in  tracing  the  series 
of  thorium  decompositions. 

555.  The  Value  of  the  Radium  Discoveries.  —  On  the  dis- 
covery of  radium,  investigations  were  at  once  started  in 
the  hope  that  its  extraordinary  radiations  might  act  as  a 
cure  for  cancer.  Its  value  for  this  purpose  is  still  in 
doubt.  This  constitutes,  so  far,  the  only  direct,  practical 
application  of  radium. 

As  sources  of  energy  the  radioactive  substances  are 
truly  remarkable.  A  bit  of  radium  in  changing  down  to 
lead  gives  out  300,000  times  as  much  energy  as  does  an 
equal  weight  of  coal  in  burning.  It  has  been  observed 
that  if  chemists  ever  succeeded  in  producing  gold  from 
the  atomic  decomposition  of  elements  of  higher  atomic 
weight,  the  energy  liberated  might  be  comparable  in  value 
to  that  of  the  gold  itself. 

The  principal  value  of  radium  has  been  in  giving  us  a 


THE    VALUE   OF  THE  RADIUM  DISCOVERIES    501 

better  understanding  of  the  nature  of  atoms.  It  is  believed 
that  all  atoms  consist  of  minute  particles,  called  electrons, 
which  are  identical  with  the  ft  emanations  of  radioactive 
bodies,  and  which  consist  of  nothing  more  nor  less  than 
negative  charges  of  electricity.  The  explosions  of  radio- 
active atoms  are  due  to  spontaneous  rearrangements  of  the 
electrons  within  the  atom.  It  is  believed  that  the  atoms 
of  all  elements  might  undergo  radioactive  transformation 
if  we  could  find  a  method  of  causing  them  to  take  place ; 
and  that  the  transmutations  of  elements  are  within  the 
range  of  final  possibility.  According  to  this  point  of 
view,  there  is  an  inexhaustible  amount  of  energy  stored  up 
in  atoms,  and  it  is  conceivable  that  some  day  this  may  be 
made  available.  It  will  be  necessary  to  find  a  way  of  in- 
ducing the  transformations  to  take  place,  just  as  it  was 
necessary  for  some  one  to  find  how  to  build  fires  to  make 
the  energy  of  fuels  available.  It  is  possible  that  all 
atoms  are  actually  undergoing  decomposition  continuously, 
but  at  such  slow  rate  that  we  are  not  able  to  observe  the 
process. 

With  the  conception  of  electrons,  chemists  are  adopting 
new  ideas  of  many  tilings,  such  as  valence  and  the  pro- 
cesses of  oxidation  and  reduction.  For  example,  a  uni- 
valent,  electropositive  element  may  be  regarded  as  made 
up  of  atoms,  which  have  a  great  tendency  to  lose  one 
electron  (a  particle  of  negative  electricity)  and  thus 
by  its  loss  to  remain  positively  charged.  A  univalent, 
electronegative  element  has  atoms  which  have  a  tendency 
to  acquire  an  electron,  and  thus  to  become  negatively 
charged.  Divalent  elements  tend  to  lose,  or  to  acquire, 
two  electrons,  and  so  on. 

The  young  student  is  likely  to  wonder  why  so  much  im- 
portance is  attached  to  a  thing  of  theoretical  interest  like 
radium.  It  appears  to  him  that  a  substance  of  which 


502  RADIUM  AND  RADIOACTIVITY 

there  arc  only  two  or  three  grams  in  the  world,  and  whose 
market  value  is  something  like  $  1,800,000  per  ounce,  can- 
not be  of  much  real  use.  But  in  taking  this  point  of  view 
he  forgets  two  things.  The  first  is  that,  in  the  main, 
practical  discoveries  and  inventions  follow  theoretical  de- 
velopment. The  second  is  that  there  is,  in  the  human 
inind,  a  need  for  understanding  the  things  that  are  about 
us,  and  that  this  need  is  a  more  permanent  part  of  human 
nature  than  even  the  desire  for  material  progress.  It  is 
this  latter  need  that  the  radioactive  discoveries  have 
satisfied  in  such  high  degree. 

SUMMARY 

Radioactivity  is  a  name  given  to  an  action  by  which  certain 
elements  give  off  continuously  large  amounts  of  energy  without 
undergoing  chemical  action. 

The  energy  is  given  off  in  the  form  of  rays  or  radiation  which 
produce  electrical  and  other  effects.  Three  types  of  these  rays 
are  recognized,  known  respectively  as  the  a,  p,  and  -y  radiations. 
They  all  have  the  power  to  penetrate  solid  substances,  that  of  the 
a  variety  being  very  slight,  that  of  the  ft  somewhat  greater,  and 
that  of  the  y  very  great. 

Following  the  discovery  of  polonium  and  radium  by  Mme.  Curie, 
it  was  shown  that  the  cause  of  radioactivity  is  a  decomposition  of 
the  atoms  of  the  elements  that  produce  the  effect. 

The  a  radiation  consists  of  positively  charged  helium  atoms. 
This  fact  constitutes  a  case  of  transmutation  of  elements. 

Since  a  radioactive  element  gradually  decomposes,  it  follows 
that  such  elements  have  a  life  period.  This  is  usually  stated  as 
the  "half  life,"  meaning  the  time  it  would  take  for  half  of  the 
atoms  in  a  given  quantity  to  decompose.  This  period  is  2500 
years  for  radium.  That  of  some  of  the  elements  is  only  a  few 


EXERCISES  503 

seconds,  that  of  others  is  millions  of  years.     The  shorter  the 
period,  the  greater  the  degree  of  radioactivity. 

Two  series  of  radioactive  elements  have  been  recognized. 
Uranium,  the  "parent"  element  in  one  series,  by  successive 
losses  of  radiation  (including  frequently,  but  not  always,  the  a  type 
helium  atoms)  passes  into  elements  of  lower  and  lower  atomic 
weight.  Radium  and  polonium  are  included  in  this  series. 
Lead  is  believed  to  be  the  end  of  this  series  of  decompositions. 

A  thorium  series  has  also  been  recognized. 

The  radium  discoveries  are  regarded  as  important  chiefly  be- 
cause they  have  brought  about  changes  in  important  chemical  theories. 
We  now  believe  that  atoms  of  all  elements  are  composed  of  large 
numbers  of  small  particles,  called  electrons.  These  are  regarded 
as  minute  charges  of  negative  electricity.  The  ft  radiation  con- 
sists of  these  particles. 

EXERCISES 

•  1.   Why  was  the  isolation  of  radium  from  pitchblende  re- 
garded as  a  brilliant  piece  of  chemical  work  ? 

2.  In  what   respects    does   radium   differ    strikingly   from 
ordinary  elements  ?     In  what  respects  does  it  resemble  them  ? 

3.  Is  it  true  that  we  could  produce  perpetual  motion  by 
means  of  radium  ?     Explain. 

4.  Distinguish  between  the  a,  /3,  and  y  radiations  emitted 
by  radioactive  elements. 

5.  Why  were  radium  and  mesothorium  I  of  especial  value 
for  purposes  of  radioactive  study  ? 

6.  What  is  meant  by  the  period  of  a  radioactive  element  ? 

7.  What  means  would  you  use  to  test  a  mineral  for  the 
presence  of  radioactive  elements  ? 

8.  What  relation  is  there  between  the  period  of  a  radio- 
active element  and  its  degree  of  activity  ? 


504  RADIUM  AND  RADIOACTIVITY 

9.   Explain  how  radioactivity  has  given  a  new  conception 
of  the  character  of  atoms  in  general. 

10.   What   is  meant  by  saying  that  enormous  amounts  of 
energy  are  liberated  by  radioaction  ? 

11.  What  ancient  idea  of  the  alchemists  has  been  revived  by 
the  radium  discoveries  ? 

12.  Name  a  radioactive  element  of  very  short  period ;  one 
of  very  long  period. 

13.  For  what  reasons  is  the  price  of  radium  very  great  ? 

14.  What  new  conception  of  valence  has  resulted  from  the 
electron  theory  of  atoms  ? 

15.  Why   is   radium   always   found   in   ores   that   contain 
uranium  ? 

16.  Why  can  we  never  expect  to  find  radium  in  more  than 
a  very  small  amount  in  any  mineral  ? 


APPENDIX 


I.    PHYSICAL  CONSTANTS 
OF  THE  IMPORTANT   ELEMENTS 


ELEMENT 

i 

I 

ATOMIC  WEIGHTS 

VALENCE 

PECIFIO  GRAVITY 

MELTING 
POINT 

BOILING 
POINT 

Approx- 
imate 

Exact 
0=16 

Water  =  1 

Air  =  l 

°C. 

°C. 

Aluminum 

Al 

27 

27.1 

III 

2.7 

657 

2200 

Antimony 

Sb 

120 

120.2 

rav 

6.6 

630 

1600 

Argon 

A 

40 

39.88 

— 

1.38 

-188 

-186 

Arsenic 

As 

75 

74.96 

mv 

5.7 

.  .  . 

<360 

volatile 

Barium 

Ba 

137 

137.37 

H 

3.8 

850 

950 

Bismuth 

Bi 

208 

208.0 

mv 

9.7 

269 

1435 

Boron 

B 

11 

11.0 

in 

2.4 

nfusible 

3500 

Bromine 

Br 

80 

79.92 

i 

3.1 

-7.3 

69 

Cadmium 

Cd 

112 

112.4 

ii 

8.6 

321 

778 

about 

Calcium 

c% 

40 

40.09 

H 

1.8 

805 

.  .  . 

amorphous 

Carbon 

C 

12 

12.00 

IV 

1.4-1.9 

infusible 

3500 

Chlorine 

Cl 

35.5 

35.46 

i 

2.49 

-102 

-33.6 

Chromium 

Cr 

52 

52.0 

II  III  VI 

6.9 

1505 

2200 

Cobalt 

Co 

59 

58.97 

H 

8.7 

1490 

Copper 

Cu 

63.6 

63.57 

ii 

8.9 

1083 

2310  £ 

Fluorine 

F 

19 

19.0 

1.26 

-223 

-187 

Gold 

Au 

197 

197.2 

in 

19.3 

1062 

25304 

Helium 

He 

4 

3.99 

— 

0.13 

-270 

-268.5 

Hydrogen 

H 

1 

1.008 

0.07 

-259 

-262 

Iodine 

I 

127 

126.92 

4.9 

114 

184 

Iron 

Fe 

56 

65.85 

n  m 

7.8 

1520 

2450  V 

Lead 

Pb 

207 

207.1 

II  IV 

11.3 

327 

1525  f 

506 


PHYSICAL    CONSTANTS 


507 


ELBMENT 

SYMBOL' 

ATOMIC  WEIGHTS 

VALENCB 

SPECIFIC  GRAVITY 

MKLTISG 
POINT 

BOILING 
POINT 

Approx- 
imate 

Exact 
O=16 

Water  =  1 

Alr  =  l 

•a 

-o. 

Lithium 

Li 

7 

6.94 

I 

0.59 

186 

<1400 

Magnesium 

Mg 

24 

24.32 

II 

1.7 

650 

1120 

Manganese 

Mn 

55 

54.93 

niv 

7.4 

1225 

1900 

Mercury 

Hg 

200 

200.0 

in 

13.6 

-38.8 

357  M 

Nickel 

Ni 

.58.7 

58.68 

ii 

8.7 

1450 

., 

Nitrogen 

N 

14 

14.01 

niv 

0.96 

—213 

-195 

Oxygen 

0 

16 

16.00 

n 

1.10 

<-218 

-182 

white 

wh 

ite 

Phosphorus 

P 

31 

31.04 

ra  v 

1.8 

44.1 

290 

Platinum 

Pt 

195 

195.2 

IV 

21.1 

1753 

.    .    . 

Potassium 

K 

39 

39.10 

i      — 

0.87 

62.5 

757  ' 

Silicon 

Si 

28 

28.4 

IV 

2.4 

1420 

3500 

Silver 

Ag 

108 

107.88 

i 

10.5 

961 

1955  A 

Sodium 

Na 

23 

23.0 

i 

0.97 

97.6 

877  * 

Strontium 

Sr 

87 

87.63 

n 

2.5 

900 

•  .  • 

rhombic 

Sulphur 

S 

32 

32.07 

II  IV  VI 

2.0 

114.5 

444.6 

Tin 

Sn 

119 

119.0 

niv  " 

7.0-7.3 

232 

1525 

Zinc 

Zn 

65 

65.37 

n 

7.1 

419 

918 

•' 


508 


APPENDIX 


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050505050505050505      |O5O5O5O5 

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iii|i  i|ii|f|lj 

SOLUBLE  AND   VOLATILE   COMPOUNDS         509 


HI.     GENERAL  RULES  FOR  SOLUBILITY 

Certain  generalizations  can  be  made  concerning  compounds  shown 
in  the  table  on  the  opposite  page.  The  exceptions  to  these  general- 
izations are  few  and  unimportant. 

1.  All  sodium,  potassium,  and  ammonium  compounds  are  soluble  in 
water. 

2.  All  nitrates,  chlorates,  and  acetates  are  soluble  in  water. 

3.  All  chlorides  are  soluble,  except  those  of  silver,  mercury  (mer- 
curous),  and  lead  (lead  slightly  soluble). 

4.  All   sulphates   are   soluble,   except   those   of   barium,   lead,   and 
calcium  (calcium  slightly  soluble).     The  silver  and  the  mercurous 
sulphates  are  only  moderately  soluble. 

5.  All  carbonates  are  insoluble,  except  those  of  sodium,  potassium, 
and  ammonium. 

6.  All   oxides   and  hydroxides  are   insoluble,  except  those  of  am- 
monium,  sodium,   potassium,   and    barium;    calcium   hydroxide    is 
slightly  soluble. 

IV.  VOLATILITY  OF  COMPOUNDS  THAT  MAY  RESULT 
FROM  DOUBLE  DECOMPOSITIONS 

1.  Compounds  volatile  at  ordinary  temperatures  : 

HC1     HBr    HF     HgS 

2.  Compounds    decomposing    at    ordinary  temperatures   yielding 
volatile  products: 

H2CO3  (H2O  +  CQ2) 
H2S03  (H20  +  SOo) 
NH4OH  (H20  +  NH3) 

3.  Compounds  volatile  at  varying  temperatures  below  338°  (boiling- 
point  of  sulphuric  acid)  : 

BOILING -POINT  BOILING-POINT 

H20,  100°        HNOg,  86° 

HC1  (aqueous  solution),       110°        HNO3  (aqueous  solution),      120° 
HBr  (aqueous  solution),      126°        HC2H8Og,  118° 

V.    APPROXIMATE  WEIGHT  OF  ONE  LITER  OF  COMMON 
GASES  UNDER   STANDARD  CONDITIONS 

Acetylene,  1.17  grams  Hydrogen  sulphide,  1.53  grams 

Ammonia,  0.77  "  Marsh  gas,  0.72  " 

Carbon  dioxide,  1.98  "  Nitrogen,  1.26  " 

Carbon  monoxide,  1.26  "  Nitric  oxide,  1.35  " 

Chlorine,  3.20  "  Nitrous  oxide,  1.98  " 

Hydrogen  chloride,  1.64  "  Oxygen,  1.44  " 

Hydrogen,  0.09  "  Sulphur  dioxide,  2.88  " 


510 


APPENDIX 


VI.    PRESSURE  OF  WATER  VAPOR,  OR  AQUEOUS 
TENSION 

(In  millimeters  of  mercury) 


TEMPERATURE 

PRESSURE 

TEMPERATURE 

PRESS  r  UK 

0.0°  C. 

4.6  mm. 

21.5°  C. 

19.1  mm. 

5 

6.5 

22. 

19.7 

10 

9.2 

22.5 

20.3 

10.5 

9.5 

23. 

20.9 

11 

9.8 

23.5 

21.5 

11.6 

10.1 

24. 

22.1 

12 

10.5 

24.5 

22.8 

12.5 

10.8 

25. 

23,5 

13 

11.2 

25.5 

24.2 

13.5 

11.5 

26. 

25.0 

.     14 

11.9 

26.5 

25.7 

14.5 

12.3 

27. 

26.5 

15 

12.7 

27.5 

27.3 

15.5 

13.1 

28. 

28.1 

16 

13.5 

.     28.5 

28.9 

16.5 

14.0 

29. 

29.8 

17 

14.4 

29.5 

30.7 

17.5 

14.9 

30 

31.6 

18 

15.4 

40 

54.9 

18.5 

15.9 

50 

92.1 

19 

16.4 

60 

149.2 

19.5 

16.9 

70 

233.8 

20 

17.4 

80 

355.4 

20.5 

17.9 

90 

526.0 

21 

18.5 

100 

760.0 

£          j(4      $j*  ^A^ji  ^*£ 

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At         /)         #/!  . 

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<**,/* 


INDEX 


References  are  to  pages. 


Heavy-face  numerals  indicate  the  principal 
reference.    ' 


Abrasive 297, 

Absolute  temperature  .  .  . 

change  of  Centigrade  to 

zero 

Absorbent  cotton 

Acetic  acid 467, 

fermentation 

production  of 

Acetone 

Acetylene 477 

series 

Acheson,  Edward  Goodrich, 

portrait      .     .     .  facing 

Acids,  active 

definition  , 83 

general  method  for  preparing 

naming  of Ill, 

.  organic 

strong 

typical  properties 

Agate 

Air,  a  mixture 

carbon  dioxide  in 

composition  of  ...... 

inert  gases  in 

water  vapor  in 

Air  slaked  lime 

Alabaster 

Alcohol,  denatured 

ethyl 

grain 

methyl 

production  of 

wood 

Alcoholic  beverages  .  .  . 

Alcohols 

Aldehydes  

Alkaline  reaction 

Allotropic  forms,  definition  . 


324 

12 
12 
12 

488 
483 
467 
483 
483 
,297 
477 

294 
158 

,  151 
81 

112 
483 
158 
82 
320 
225 
227 
224 
228 
226 
336 
338 
480 
480 
480 
480 
466 
480 
467 
479 
481 
139 
194 


Alloys,  fusible 265 

Alum 416 

ammonium 417 

chrome 416 

iron 379 

potassium 416 

Aluminates 414 

Aluminum  .     .     Chap.  XXXIV,  412 

alloys 415 

bronze 415 

magnalium  metal .    .     .     .  415 

electrolytic  preparation  of      .  412 

foil ..414 

occurrence 412 

powder 414 

properties,  chemical  ....  414 

physical 413 

uses 414 

Aluminum  compounds 

Chap.  XXXIV,  412,  416 

acetate 418 

hydroxide 417 

preparation 417 

properties 417 

uses 418 

lakes 418 

mordant 418 

water  purification     .     .  418 

potassium  sulphate    ....  416 

silicates    ........  420 

Amalgamation     process     for 

gold 404 

Amalgams 351 

Amethyst 319 

Ammonia    .........  233 

commercial  production  .     .     .  233 

formation  in  nature  ....  233 

fountain 236 

household 237 


511 


512 


INDEX 


References  are  to  pages. 


Ammonia  —  Continued 

preparation,  from  coal  .     .     •     233 
Haber  and  Le  Rossignol     .    234 

laboratory 235 

Ostwald 234 

properties,  chemical  ....    236 

physical 235 

uses 237 

Ammonium  alum 417 

chloride 239- 

hydroxide 237 

nitrate 239 

radical 237 

salts 238 

sulphate .233 

Anaesthetics,  chloroform      .     .    479 

ether 487 

methyl  chloride 479 

nitrous  oxide 239 

Analysis,  as  type  reaction     .     .    118 
definition 43 

Anhydride,  acid,  definition  .     .    207 
basic,  definition 207 

Anode 33 

Antifriction  metals    ....    264 

Antimony 264 

alloys 265 

black 264 

Aqua  fortis 242 

Aquaregia 248 

Aqueous    tension,    correction 

for 17 

defined 17 

table  of 21,  510 

Argon 224 

Arrhenius,  Svante    August, 

portrait    .    .     .  facing    152 

Arsenic 263 

compounds 263 

Asbestos 343 

platinized 213 

Atmosphere    .    .    .  Chap.  XXI,  221 

Atom,  definition 65 

Atomic        and        Molecular 

weights  .    .     .  Chap.  XI,  95 

Atomic  hypothesis    ....      64 
value  of 68 

Atomic  weights,  table  of    .    .    506 

Atoms  and  molecules 

Chap.  VII,  64 

Atoms,  number  in  molecule  of 


compound,        determina- 
tion of 

number  in  molecules  of  gases 
Avogadro's  hypothesis      .     . 


90 


Babbitt  metal .264 

Bacteria,  nitrifying      ....    252 

Baking  powder 310 

Baking  soda 181,310 

Barley  sugar 491 

Barium  chloride 217 

peroxide 59 

sulphate 217 

Barometer 11 

Base  bullion 432 

139 

definition 139,  152 

Basic    lining.    Bessemer    con- 
verter     366 

Bauxite 412 

Beer 466 

Benzene 478 

Benzine 464 

Benzol      .........    478 

Berzelius,  Johann  Jacob,  por- 
trait   facing    108 

Bessemer  converter  :    ...    366 

basic  lining 366 

process  for  copper      ....    386 

for  iron 365 

Bessemer  steel 365 

Beverages,  alcoholic  ....  466 
Bichloride  of  mercury  ...  353 
Binary  compounds  ....  109 

Bismuth 264 

Blast  furnace,  for  copper     .     .    386 

for  iron 360,  361 

Bleaching,  by  chloride  of  lime  .    340 

by  chlorine 75 

by  hydrogen  peroxide    ...      60 

by  sulphur  dioxide     ....    208 

Bleaching  powder      .    .    .76,  340 

Blister  copper -386 

Blowpipe,  oxyhydrogen    ...      40 

Blue  prints 380 

Boiler  scale 331 

Boneblack 293,  462 

Borax 326 

cleansing  agent 327 

uses,  bead  tests 327 

Bordeaux  mixture     ....    392 


INDEX 


513 


References  are  to  pages. 


Boric  acid 326 

Boron  .    .    .  Chap.  XXVII,  319,  326 

Boyle's  Law 14 

Brandy 467 

Brass 348 

Bread,  raising  of  .     .     .     .     .     .  310 

by  yeast    ...•.;..  465 

Bricks 420 

Brimstone 192 

Britannia  metal      ...      264,430 

Bromine 268 

occurrence 268 

preparation,  commercial    .     .  268 

laboratory 269 

properties,  chemical  ....  271 

physical 270 

replacement  of 273 

test  for 274 

uses 271 

water 271 

Bromides,  test  for 274 

Bronze 348,430 

aluminum 415 

Bunsen  burner 26 

Bunsen,     Robert     Wilhelm, 

portrait     .     .    .  facing  26 

Burning? 6 

Butane 476 

Cairngorm  stone 320 

Calcite 331 

Calcium  .    .    .     Chap.  XXVIII,  329 

light 336 

preparation   . 329 

properties,  chemical  ....  330 

physical 330 

Calcium  compounds 

Chap.  XXVIII,  329 

bicarbonate 309,  337 

carbide      ........  297 

carbonate      .    /    .    .    .    .    •  330 

occurrence 330 

uses      .    ./ 333 

varieties 330 

cyanamide     ....  224,  234,  252 

from  calcium  carbide     .    .  234 

hydroxide,  properties     .     .     .  336 

uses 336 

nitrate 250 

phosphate 263 

sulphate 338 


superphosphate 340 

Calculations,  chemical 

Chap.  XIV,  125 

volume 127 

weight 125 

weight  and  volume    ....    129 

Calomel 352 

Calorie,  definition 50 

Cannel  coal  ^ 290 

Caramel 491 

Carat,  definition 405* 

Carbides 297,  324 

Carbohydrates 487 

Carbolic  acid 480 

Carbon    ....     Chap.  XXV,  288 

allotropic  forms 294 

amorphous 294 

character  of 288 

compounds,  classes  of 

Chap.  XXXIX,  474 
industrial    Chap.  XXXVIII,  459 

sources' 460 

dioxide,  cycle  in  nature      .     .    227 

in  air 227,  308 

occurrence 305 

preparation 305 

properties,  chemical .     .     .    307 

physical 306 

test  for 309 

uses 310 

disulphide 298 

monoxide 311 

in  water  gas      .     .     .     *    .    313 

preparation 311 

properties,  chemical .     .     .    312 

physical 312 

physiological    .     .     ...    313 

occurrence 288 

oxides  ....   Chap.  XXVI,  305 
properties,  chemical  ....    295 

physical 295 

tetrachloride .479 

use 298 

Carbonic  acid 308 

Carborundum     ....    297, 324 

Carnallite 343 

Cast  iron,  composition  of      .     .    363 

gray 363 

manufacture  of      .....    360 
properties 363 


514 


INDEX 


References  are  to  pages. 


Cast  iron—  Continued 

white 363 

Castner,    Hamilton    Young, 

portrait      .     .     .  facing  172 

Catalytic  agent 30 

Cathode 33 

Caustic  alkalies 174 

potash 176 

soda ,  ....  174 

Caves,  formation  of    '  .     .     .     .  332 

Celluloid 489 

Cellulose 488 

acetate 488 

Cement,  hydraulic 423 

burning .     .  423 

hardening 423 

natural 423 

setting  of  ........  423 

Chalcedony 320 

Chalcopyrite 385 

Chalk,  native 331 

Charcoal,  animal      .   '.     .    .     .  293 

wood 292 

Charles'  Law 12 

Chemical  change 1 

Chemical       formulas       and 

names      .    .    Chap.  XII,  102 

Chile  saltpeter 185 

China 421 

firing  of 422 

Chloride  of  lime 340 

Chlorides 83 

insoluble 508 

test  for 84 

Chlorine Chap.  VIII,  71 

action  with  water 75 

with  hydrogen 74 

preparation  by  electrolysis     .  71 
by    oxidation     of    hydro- 
chloric acid 72 

properties,  chemical  ....  73 

physical    .......  73 

occurrence 71 

uses 75 

Chloroform 479 

Chlorplatinic  acid 409 

Choke  damp 395 

Chromates 441 

Chrome  alum 416 

steel 369 

yellow 436,  442 


Chromic  acid 442 

anhydride 442 

chloride 441 

oxidation  of 442 

oxide 441 

Chromite 440 

Chromium    Chap.  XXXVI,  439,  440 

compounds 441 

occurrence 440 

oxide 441 

preparation 440 

properties 440 

uses 441 

Chromous  chloride    ....  442 

Cinnabar 350 

Citric  acid 485 

Clay 412, 420 

Coagulum,  in  water  purifica- 
tion   418 

Coal 290 

anthracite 290 

bituminous 290 

cannel 290 

composition  of 291 

formation  in  nature  ....  290 

soft .290 

destructive  distillation  of  460 

Coal  gas  (illuminating)    ...  460 
Coal   stove,    chemical   action 

in       ........  311 

Coal  tar 461 

Cobalt      .      Chap.  XXXVI,  439,  446 

chloride 446 

cyanides,  double  (potassium)  447 

extraction 446 

glance 446 

nitrate 447 

test  for  zinc 348 

ores 446 

properties 446 

speiss 446 

sulphide 447 

Coins,  copper  (bronze)      .     .     .  430 

gold 405 

nickel 446 

silver 399 

Coke 293 

Collodion 489 

Colloid,  definition 406 

Colloids,  importance  of    ...  407 

production  of 406 


INDEX 


515 


References  are  to  pages. 


Combining  weights 

Chap.  V,  43,  45 

Combustion 23 

spontaneous 26 

Compound,  definition.     ...  6 

Concrete     .........  424 

reen forced 424 

Condenser,  Liebig 51 

Conservation  of  mass    ...  64 
Contact     process    (sulphuric 

acid) 210 

Converter,  Bessemer  ....  366 

Copper    .     .     .     .  Chap.  XXXII,  384 

blister 386 

compounds 

Chap.  XXXII,  384,  390 

electro-refining 388 

matte 385 

metallurgy 385 

native 384 

occurrence    .......  384 

ores .385 

oxides 390 

poling 387 

properties 389 

sulphate 391 

preparation 391 

properties 392 

uses 392 

uses 389 

Copperas 379 

Coquina 331 

Corn,  products  obtained  from    .  469 

Corrosive  sublimate      .     .     .  353 

Corundum 412 

Cream  of  tartar      .     .    .     310, 485 

Crockery 420 

Crucible  steel     ......  368 

uses 369 

Cryolite 412 

Crystallization,  water  of,  defi- 
nition     57, 61 

Crystalloids 406 

Crystals 57 

Cupellation 397 

Cupric  oxide 391 

Cuprous  oxide 390 

Curie,  Marie  Slodowska,  por- 
trait     ....  facing  494 
Cyanamide      ....  224,  234,  252 
Cyanide  process  for  gold  .     .  405 


Cycle,  carbon  dioxkle-oxygen    .  227 

diagrams  for 231 

nitrogen 227 

Dalton,  John,  portrait    facing  44 
Davy,    Sir    Humphry,    por- 
trait   ....  facing  136 
Decomposition,  as  type  action  118 

Decrepitation .179 

Definite  proportions,  law  of  .  45 

Deliquescence 57 

Deliquescent  substances  .    .  61 

Denatured  alcohol     ....  480 

Density,  definition 95 

Depolarizer 439 

Destructive    distillation    of 

bones 462 

of  coal 460 

of  wood    ........  462 

Dextrine 487 

Dextrose 466 

Dialysing  membranes   ...  406 

Diamond 295 

artificial 295 

Diastase 466,488 

Diatomaceous  earth      .     .    .  320 

Dichromates 441 

Difference  in  level,  correction 

for 16 

Disinfecting,      by       bleaching 

powder 340 

chloride  of  lime 340 

chlorine 77 

formaldehyde    ......  482 

hydrogen  peroxide      ....  60 

ozone 29 

sulphur  dioxide 208 

Dissociation,  in  electrolytes     .  148 

of  ammonium  chloride   .     .     .  239 

Distillation 51 

destructive 293,460 

of  bones 462 

of  coal 460 

of  wood 462 

fractional 463 

of  petroleum 463 

Dolomite 331,  343 

Double  salts 416 

Duncan,    Robert    Kennedy, 

portrait     .     .     .     facing  464 

Dutch  process  for  white  lead  435 


516 


INDEX 


References  are  to  pages. 


Dynamite 253,  48G 

Earthenware 420 

Efflorescence 57 

Efflorescent  substances     .    .  61 

Electric  furnace 297 

Electrolysis 144 

explanation  of 150 

of  water 33 

Electrolytes 144 

chemical  activity  of  ....  149 

dissociation  of 148 

Electrolytic  refining  of  cop- 
per    388 

Electroplating,  with  gold   .     .  406 

nickel 445 

silver .  399 

Element,  definition 6 

Elements,  gaseous,  number  of 

atoms  in  molecule  ...  90 

table  of 506 

physical  constants,  table  of    .  506 

Emery 412 

Enzymes 465 

Epsom  satts 343 

Equations,  chemical   Chap.  XIII,  116 

balancing  of 117 

calculations         of       relative 

weights  from      ....  125 

significance  of 116 

Equilibrium,  chemical 

Chap.  XVII,  160 

dynamic 160 

Esters 485 

Etching  of  glass 283 

Ethane 476 

Ether 487 

sulphuric 487 

Ethereal  salts 485 

Ethyl  alcohol 480 

Explosives 253 

Families  of  elements     .     .    .  454 
Faraday,  Michael,  portrait 

facing  148 

Fats 486 

Fehling's  solution 391 

Feldspar 420 

Fermentation 465 

Ferric,  ammonium  alum   .     .     .  378 

ammonium  citrate     ....  I 


chloride 377 

ferrocyanide 380 

hydroxide 376 

ions 375 

oxide 376 

salts,  reduction  of      ....    378 

sulphate 379 

tannate 379 

Ferricyanides 380 

Ferrocyanides 379 

Ferromanganese 439 

Ferrous  bicarbonate     ....    377 

carbonate 377 

chloride 377 

ferricyanide 380 

hydroxide 377 

ion    . 375 

oxide 376 

salts,  oxidation  of      ....    378 

sulphate 378 

tannate 379 

Fertilizers 186,  224,  340 

Films,  photographic .     .     .     .401,488 

Filter  paper 488 

Firebricks 420 

Fire  extinguisher 310 

Fire  extinguishers,  automatic    265 

Fire  damp 477 

Fireprooflng,  cotton  goods  by 

sodium  stannate     .     .     .    431 
Fixation  of  nitrogen      ...    251 

Flame,  bunsen 27 

candle 298 

gas 301 

Flashlight  powder     .     .      344,414 

Flint     .     .     .     • 320 

Fluorine 280 

preparation  of 281 

properties  of 282 

Fluor  spar 282 

Flux,  definition 359 

Formaldehyde 482 

Formalin 483 

Formic  acid 311 

Formulas     ....    Chap.  XII,  102 

calculation  of 104 

significance  of   ......    103 

structural 474 

Fractional  distillation    ...    463 
Frasch,  Herman,  portrait 

facing  190 


INDEX 


517 


References  are  to  pages. 


Prasch  method  (sulphur)    .     .  189 

Freezing-  mixture 54 

Freezing  point,  effect  of  dis- 
solved solids  on      ...  145 

Fructose 489 

Fungicide    ........  393 

Furnace,  blast,  copper      ...  386 

blast,  iron 381 

electric 297 

glass .     .  322 

open  hearth  steel 366 

reverberatory    ....      364,431 

Fuse  wire 434 

Fusible  metals 265 

Fusion,  heat  of 50 

Galena 431 

electrolytic  reduction  of     .     .  432 

Galvanized  iron 348 

Gas,  definition 7 

illuminating 460 

marsh 474 

natural 292 

oil 464 

producer 314 

volume,  corrections  for  ...  13 
correction  for  difference  in 

level 16 

correction  for  pressure  .     .  15 

correction  for  temperature  14 

correction  for  water  vapor  17 

water 313 

Gases    and    their   measure- 
ment    ....   Chap.  II,  10 

Gases,  pressure  of 10 

vapor  density  of 96 

weight  of  one  liter  of      ...  509 

calculation  of 129 

Gasoline 464 

Gay-Lussac,  law  of      ....  89 

German  silver 348 

Gin 467 

Girod  furnace 370 

Glass,  bohemian   ....      322,  324 

colored 324 

composition  of 322 

crown 322,  324 

cut 323 

etching  of 283 

flint 322,324 

furnace 322 


manufacture  of 322 

plate 323 

window 323 

Glaze  for  pottery 420 

Glucose 488,  489 

from  starch 487 

test  for 391 

Glycerine 468 

Gneiss 321 

Gold     .    .      Chap.  XXXHI,  396,  404 

amalgamation  of 404 

chloride 405 

coins 405 

colloidal 406 

leaf 405 

metallurgy 404 

nuggets 404 

occurrence 404 

properties  of 405 

recovery  from  copper     .     .     .  389 

separation  of 404 

uses 405 

Grain  alcohol 480 

Gram-molecular  volume  .     .  98 

Gram-molecular  weight    .    .  97 

Granite 321 

Graphite 294 

Guano 340 

Guncotton 254,  489 

Gypsum 338 

Haber  and  Le  Bossignol  pro- 
cess for  ammonia  .    .  234 

Hall,  Charles  Martin,  portrait 

facing  412 

Halogens     .     .    .    Chap.  XXIV,  268 

as  a  group 278 

relative  replacement  of  ...  279 

tabular  comparison  of    ...  278 

Hard  waters 309 

action  with  soap 486 

permanent 309 

softening  by  lime 337 

temporary 309 

Heat,  of  formation 278 

definition 279 

relation  to  chemical  action  280 

of  fusion 50 

of  neutralization 155 

of  vaporization 50 

Helium  in  air 230,496 


518 


INDEX 


References  are  to  pages. 


Hematite 359 

Heroult  furnace 370 

Hornblende 343 

Horn  silver 396 

Humidity  of  air 227 

Hydraulic  cement 423 

Hydriodic  acid 277 

Hydrobromic  acid      ....  271 

preparation 271 

properties 273 

uses 273 

Hydrocarbons     ....      288,474 

definition 491 

series,  acetylene 477 

aromatic 477 

benzene 477 

benzol 477 

marsh  gas 475 

methane 475 

olefiant 47(5 

paraffin 475 

Hydrochloric  acid      .  Chap.  IX,  80 

preparation 80 

uses 84 

Hydrofluoric  acid 282 

uses 283 

Hydrogen Chap.  IV,  33 

number  of  atoms  in  molecule  91 
preparation,    electrolysis    of 

water 33 

metals  on  water    ....  34 

replacement  in  acids      .     .  35 

properties,  chemical  ....  37 

physical 37 

uses 39 

Hydrogen  chloride     ....  80 

composition,  volumetric     .     .  84 

preparation 80 

properties,  chemical  ....  82 

physical 81 

Hydrogen  peroxide  ....  59 

preparation 59 

properties 59 

uses 60 

Hydrogen  sulphide    ....  197 

preparation 197 

properties,  chemical  ....  198 

physical 198 

Hydrogenation  of  oils   ...  40 

Hydrolysis      .    ? 182 

Hygroscopic  substance     .    .  61 


Hypo 

Hyposulphite  of  soda    .    .    . 

Ice 

artificial 

Iceland  spar 

Illuminating  gas,  coal  .  .  . 

water 

Indian  red 

Inert  gases  in  the  atmos- 
phere   

Infusorial  earth 

Ink,  iron 

Insolubility,  actions  go  to  an 

end  through 

Invertase 

Iodides 

Iodine  


occurrence     .     .     . 
preparation   . 
properties,  chemical 

physical  .  .  . 
tests  for  .... 
tincture 


uses 

lodoform 

lonization 

effect  of  dilution  on  .... 

evidence  of,  freezing  point 
osmotic  pressure  .... 

in  other  than  water  solution  . 

of  acids  and  bases      .... 
Ions 

charges  carried  by     .... 

distinguished  from  atoms  .     . 

valence  of 

Iridium 

Iron Chap.  XXX 

carbide      ........ 

cast,  composition  of  .... 
manufacture  of  .... 
properties  of 

compounds,    see    Ferric   and 
Ferrous. 

galvanized 

ions 

magnetic  oxide 

occurrence     

ores,  formation  of  .... 
smelting  of 

Pig 


401 
402 

52 
238 
331 
460 
313 
376 

228 
320 
379 

163 
490 
277 
275 
275 
275 
276 
275 
277 
275 
277 
479 
150 
152 
146 
150 
157 
151 
149 
155 
150 
156 
407 
,358 
371 
363 
360 
363 


348 
375 
376 
358 
358 
a59 
361 


INDEX 


519 


References  are  to  pages. 


Iron  —  Continued 

properties  of  pure      ....    375 

Russia 376 

rust 24,  377 

wrought 364 

composition  of  .....    365 
manufacture  of     ....    364 

properties  of 365 

uses 365 

Iron  and  steel,  classification  of 

372,  373 


Jasper 


320 

343 
420 
275 
464 
481 
334 


Kainite 

Kaolin 

Kelp 

Kerosene 

Ketones 

Kiln,  lime,  long  rtame    . 

rotary 334 

pottery      422 

Kindling  temperature   ...  25 

Krypton 229 

Lakes 418 

Lampblack 291 

Salsburgh  process 292 

Laughing  gas 239 

Lavoisier,  Antoine  Laurent, 

portrait      .     .     .   facing  2 

Lavoisier's  experiment      .    .  3 

Law  of  definite  proportions  45 

explanation  of 66 

Lead    .    .    .  Chap.  XXXV,  428,  431 

acetate,  basic 436 

alloys  of 434 

burning 40 

carbonate,  basic 435 

chromate 436,  442 

dioxide 435 

metallurgy  of 431 

ore 431 

oxides 434,435 

pig 432 

pipe 433 

poisoning 433 

properties .  432 

red 435 

reduction,  electrolytic    .     .     .  432 

sheet 434 


shot .434 

sulphide 431 

tree 433 

uses 433 

white 435 

Levulose 466 

Life,  relation  of  oxygen  to     .     .  28 

Lignite 290 

Lime 333 

air  slaked 336 

chloride  of 340 

kiln,  long  flame     .....  334 

rotary 334 

light 336 

manufacture  of 334 

quick 333 

slaked 336 

uses 336 

water 336 

Limestone 331 

caves 332 

Limonite 359 

Liquid,  definition 7 

Litharge 434 

Lithium 138 

Lubricating  oils 464 

Lunar  caustic 400 

Magnalium 415 

Magnesite 343 

Magnesium     .    .    Chap.  XXIX,  343 

compounds  of 344 

occurrence 343 

preparation  of 343 

properties 343 

uses 343 

Malachite 385 

Malt 466,  488 

Maltose 46b,  488 

Manganates 440 

Manganese      .     Chap.  XXXVI,  439 

.compounds  of 439 

dioxide 439 

preparation  of 439 

properties  of 439 

steel 369 

Marble 330 

Marie 423 

Marsh  gas 474 

Mass  action,  law  of     ....  165 

applications  of 166 


520 


INDEX 


References  are  to  pages. 


J,  conservation  of   ....  64 

Massicot 434 

Matches 261 

friction 261 

impregnated 262 

safety 262 

Matte,  copper 385 

Matter,  definition 68 

Melting  point  of  elements     .  506 
Mendelejeff,   Dimitri  Ivano- 

vitch,  portrait  .  facing  450 

Mercuric  chloride      ....  353 

Mercuric  oxide 353 

decomposition  of 5 

Mercurous  chloride  ....  352 

Mercury ....    Chap.  XXIX,  343 

compounds  of 352 

extraction  of 350 

occurrence 350 

properties,  chemical  ....  351 

physical 351 

uses 352 

Metals  heated  in  air  .     .     .     .  •  2 

Meteorites 358 

Methane 474 

Methyl  alcohol 480 

Methyl  chloride 479 

Mica 321 

Mineral,  definition 345 

Minium 435 

Mirrors,  silvering  of     ....  399 
Miscible    substances,    defini- 
tion    53 

Molasses 466 

Molecular  composition  Chap.  X,  89 
Molecular  weights     .  Chap.  XI,  95 

definition 96 

determination  of 96 

Molecules  (and  atoms) 

Chap.  VII,  64 

definition 65 

Molybdenum  steel     ....  369 

Monocalcium  phosphate   263,  340 

in  fertilizers 263 

Monochlormethane   ....  478 
Mordant,  aluminum  hydroxide 

as 418 

copper  sulphate  as     ....  393 

stannous  chloride  as  ....  430 
Morley,  Edward,  portrait 

facing  96 


Mortar,  hardening  of    ....  338 

Multiple  proportions,  law  of  .  60 

explanation  of 67 

Muriatic  acid 82 

Names,  chemical,  Chap.  XII,  102, 109 

Naphtha 464 

Nascent  state,  definition      .     .  77 

Neon 229 

Neutralization 139 

explanation  of 153 

heat  of 155 

products  of 154 

Nickel .     .      Chap.  XXXVI,  439,  443 

alloys 446 

coins 446 

extraction  of      , 443 

matte 444 

occurrence 443 

ores 443 

plating 445 

properties 445 

speiss 444 

steel 369,446 

Nickel  carbonyl 445 

sulphate 446 

Nitrates 249 

preparation  of 250 

tests  for 250 

Nitrate  of  sodium 249 

of  potassium 249 

Nitre 185 

Nitric  acid 242 

action  with  metals     ....  247 

as  oxidizing  agent      ....  246 

preparation  of 242 

from  air 243 

properties,  chemical  ....  245 

physical 245 

reduction  products  of     ...  246 

uses       248 

Nitric  anhydride 242 

Nitric  oxide 240 

Nitrides 224 

Nitrification 252 

Nitrites 186,  251 

Nitrocellulose     ....     254, 489 

Nitrogen     ....  Chap.  XXI,  221 

compounds    .     .     Chap.  XXII,  233 

cycle 231 

fixation  of                                .  251 


INDEX 


521 


References  are  to  pages. 


Nitrogen  —  Continued 

group    ....   Chap.  XXIII,  257 

occurrence 221 

oxides  of 239,  241 

preparation 221 

properties,  chemical  ....    223 

physical 222 

Nitrogen  fixing  bacteria   .    .    252 
Nitroglycerine    ....    253,485 

Nitrous  acid 242 

Nitrous  anhydride      ....    242 

Nitrous  oxide 239 

Nomenclature 109 

acids Ill 

binary  compounds      ....    109 

salts Ill 

Non-electrolytes 144 

Occlusion    . .407 

definition 37 

Ochre,  yellow 376 

Oleic  acid 486 

Oil  coke 293 

Oil  of  wintergreen      ....  485 

Oils,  animal  and  vegetable     .     .  486 

hydrogenation  of 40 

Onyx 320 

Opal 320 

Open  hearth  steel 366 

uses  of 368 

Ore,  definition 345 

Organic  chemistry,  definition  459 

Orpiment 264 

Osmotic  pressure 147 

analogy  to  gas  pressure      .     .  148 
Ostwald  process  for  ammo- 
nia    234 

Oxalic  acid 484 

Oxidation 24,  378 

slow 24 

Oxides,  of  carbon     Chap.  XXVI,  305 

of  nitrogen 239 

of  sulphur     .     .     .    Chap.  XX,  204 

Oxidized  silver 398 

Oxygen Chap.  Ill,  22 

number  of  atoms  in  molecule 

of 92 

occurrence  of 28 

preparation  of,  electrolysis  of 

water 38 

from  mercuric  oxide      .     .  22 


from  potassium  chlorate    .  22 

properties,  chemical  ....  23 

physical 23 

relation  to  life 28 

Oxhydrogen  blowpipe  ...  40 

Ozone 29 

Painters'  colic 433 

Palmitic  acid 486 

Paraffin 465 

series 475 

Parafllns,  table  of 476 

Paris  green 264 

Parkes'  process  for  silver     .  396 

Peat 290 

Percentage  composition,  cal- 
culation of 107 

Periodic  law       Chap.  XXXVII,  450 

groups  of  elements     ....  454 

history  of  development  .     .     .  450 

long  periods 454 

short  periods 453 

statement  of  the  law      .     .     .  453 

table 452 

vacant  spaces  in  ....  456 

value  of 456 

Permanganates 440 

Petrified  wood 321 

Petroleum,  cracking  of    ...  464 

distillation  of 463 

products  of  distillation  of  .     .  464 

refining  of 464 

Pewter 264,430 

Phosphates 263 

Phosphor  bronze 261 

Phosphoric  acid 263 

anhydride 262 

oxide 262 

Phosphorus 258 

allotropic  forms 259 

occurrence 258 

poisoning 260 

preparation 258 

red    . 260 

sesquisulphide 261 

uses 261 

white 259 

Photographic  exposure     .    .  401 

development 401 

filing 402 

negative 402 


522 


INDEX 


References  are  to  pages. 


Photographic  —  Continued 

paper,  sensitizing  of  ....  402 

positive 403 

printing 402 

toning 402 

Photography 401 

Physical  change 1 

Physical  constants,  table  of    .  506 

Pig  iron .361 

Pig  lead 432 

Pitchblende 495 

Plaster  of  Paris 338 

casts 339 

Platinized  asbestos    ....  209 
Platinum     .  Chap.  XXXIII,  396,  407 

black 408 

compounds  of 409 

finely  divided 212 

occurrence 407 

properties 407 

spongy 408 

uses 408 

Plugs,  fusible 265 

Poisoning,  phosphorus      ...  260 

Poling  of  copper 387 

Polonium 495 

Porcelain 421 

firing  of 422 

Potassium  .     .    Chap.  XV,  135,  140 
acid  tartrate      ....     310,  485 

alum 416 

carbonate 182 

chlorate 22 

chloride 179 

chromate  .     .     .     .     .     .     .     .  441 

compounds    .     .    Chap.  XVIII,  171 

cyanide 400 

dichromate 441 

ferricyanide .     .     .  .  .     .     .    .  380 

ferrocyanide 379 

hydroxide,  preparation  ...  172 

properties 174 

uses 175 

manganate 440 

nitrate,  occurrence    .     .      184,  249 

preparation 185 

uses 185,  249 

permanganate 440 

Pottery 420 

firing  of 420 

glazes   .    .    .    , 420 


kiln 422 

Powder,  smokeless 254 

Pressure,  gas,  correction  for     .  14 

Prest-O-Lite 483 

Priestley,  Joseph,  portrait 

facing   2 

Producer  gas 314 

Propane 476 

Proteins 288 

Prussian  blue 380 

Puddling  process  .....  364 

Pyrolusite 439 

Quartz 319 

Quicklime 333 

uses 336 

Quicksilver 351 

Radioactive  decay  ...     .     .    .497 

life  period     .......  499 

series 498 

Radioactivity      .     .     Chap.  XL,  494 

nature  of 495 

Radium Chap.  XL,  494 

clock 497 

discoveries,  value  of  ....  500 

emanations,  three  types  of      .  495 
Ramsay,  Sir  William,  portrait 

facing  228 
Reacting  quantities,  calculated 

from  equations  ....  125 
volumes,      calculated     from 

equations 127 

weights  and  volume  weights 
of  gases,  relation  be- 
tween    90 

definition 47 

method  of  determining       .  48 
relation  to  atomic      ...  67 
Reactions  that  go  to  an  end, 
through  heat  of  forma- 
tion    280 

through  insolubility  ....  163 

through  non-ionization  .     .     .  164 

through  volatility 162 

Realgar 264 

Red  lead 435 

Red  prussiate  of  potash  .     .  380 

Red  short  steel 363 

Reducing  agent,  definition  .     .  39 

Reduction,  definition   ....  39 


INDEX 


523 


References  are  to  pages. 


Refrigeration,  artificial   ...  238 
Regenerative    heating    sys- 
tem    366 

Replacements,      relation      to 

heats  of  formation      .     .  280 
Reverberatory  furnace      .    .  364 
Reversible  reactions   119,  122,  160 
Richards,  Theodore  W.,  por- 
trait   facing  96 

Roasting,  definition      ....  346 

Rochelle  salt       311 

Rock  crystal 319 

Rose's  metal 265 

Rouge 376 

Ruby 412 

Rum .467 

Russia  iron 376 

Rust,  iron 24,  377 

Saccharose 489 

Salsburgh  process  for  lamp- 
black      292 

Salt,  common 175 

definition 83 

Saltpeter,  Chile  ....     185,  249 

ordinary 185,  249 

Salts,  double 416 

ethereal 485 

naming  of Ill,  113 

solubility  of 508 

Sand 320 

Sandstone 320 

Sapphire 412 

Saturation  (in  solutions)  ...  53 

Schweitzer's  reagent    ...  488 

Seggar 422 

Self-hardening  steel  ....  369 

Seltzer 310 

Series,  hydrocarbon  (see  Hydro- 
carbon Series). 

radioactive 498 

uranium 498 

thorium     .• 499 

Shaking  out,  halogen  tests  .    .  274 

Shot,  lead     ........  434 

Siderite 358 

Sienna,  burnt 376 

raw 376 

Silica 319 

vitrified 321 

Silicates  .                                  .  321 


Silicic  acid 322 

Silicon      ....  Chap.  XXXII,  319 

carbide 297,  324 

dioxide,  properties     ....    320 

uses 320 

varieties 319 

fluoride 326 

occurrence 319 

Silver  ....      Chap.  XXXIII,  396 

alloys 399 

bromide .401 

chloride 396,400 

cleaning  of 398 

coins 399 

compounds  in  photography    .    401 

cupellation 397 

horn 396 

iodide 401 

metallurgy 396 

nitrate 400 

occurrence 396 

oxidized 398 

plating 399 

properties,  chemical  ....    398 

physical 398 

refining  by  electrolysis  .     .     .    397 

sterling 399 

tarnishing  of 398 

uses 399 

Slag 361 

Slaked  lime 336 

Smelting,  definition      ....    359 

Smithsonite 345 

Smokeless  powder    ....    254 

Soap 468, 486 

action  with  hard  water  .    .     .    486 

cold  process 468 

floating 469 

hard 468 

manufacture  of 468 

powders 469 

rosin 468 

salting  out 468 

semi-boiled 468 

soft  soap .486 

Soda 181 

ash 181 

Sodium Chap.  XV,  135 

action  with  water 136 

bicarbonate,  preparation,  Sol- 

vay  process 180 


524 


INDEX 


References  are  to  pages. 


Sodium  —  Continued 

uses 182 

carbonate,  preparation  .     .     .  180 

uses 182 

chloride,  crystalline  form  .     .  178 

extraction  from  sea  water  .  178 

properties 178 

purification 178 

sources 175 

uses 178 

compounds    .     .    Chap.  XVIII,  171 

cyanide 405 

dichromate 441 

hydroxide,  preparation,  elec- 
trolytic        172 

preparation,  lye  process     .  174 

properties 174 

uses 174 

nitrate 184 

properties 185 

uses 185 

nitrite 186 

peroxide 175 

preparation 135 

properties,  chemical  ....  136 

physical 136 

silicate 321 

stearate 486 

tetraborate 326 

thiosulphate 402 

uses 137 

Solder 430,434 

Solid,  definition 6 

Solubilities,  table 508 

Solubility,  general  rules  for      .  509 

relation  to  pressure    ....  54 

relation  to  temperature      .     .  53 

Solute,  definition 52 

Solution Chap.  XVI,  143 

definition 61 

saturated 53 

supersaturated 55 

water  and      ....  Chap.  VI,  50 

Solutions,  conducting  power  of  143 

conducting  power,  test  for      .  143 
Solvay,  Ernest,  portrait 

facing  172 

Solvay  process .180 

Solvent,  definition 52 

Special  steels 369 

Specific  gravity,  definition     .  96 


Spectra frontispiece 

Spectroscope 138 

Spectrum  analysis     ....  137 

Spelter 346 

Spiegeleisen 366 

Spongy  platinum 408 

Spontaneous  combustion      .  26 

Springs,  sulphur 200 

Sprinklers,  fire,  automatic  .     .  265 

Stalactites 333 

Stalagmites 333 

Stannic  chloride 430 

sulphide 431 

Starch 469,487 

formation  in  nature  ....  308 

manufacture  of 470 

Stassfurt  deposits      .     .      179,  268 

Steam 52 

gauge 10 

Stearic  acid 486 

Stearin 486 

Steel Chap.  XXX,  358 

Bessemer 365 

chrome 369 

cold  short 364 

crucible 368 

uses 369 

electric  refining 370 

manganese 369 

molybdenum 369 

nickel 369,446 

open  hearth 366 

manufacture 366 

uses 368 

red  short 363 

special 369 

self-hardening 369 

tempering  of 371 

tungsten 369 

vanadium 369 

Steel  and  iron,  classification  of  372 

Sterling  silver    ......  399 

Stoneware       ........  420 

Storage  batteries 435 

Stove  linings 420 

Styptic    .    . 417 

Sublimation,  defined   ....  276 

Substitution  products  ...  478 

Sugar,  barley 491 

beet '470,489 

cane 470,489 


INDEX 


525 


References  are  to  pages. 


Sugar—  Continued 

fruit 489 

grape 489 

manufacture  of 470 

maple 490 

refining     .........  470 

sources 470 

Sulphates,  insoluble     ....  509 

test  for 216 

Sulphides    .     .  Chap.  XIX,  189,  196 

formation  of 199 

Sulphites 205, 207 

Sulphur  .'....  Chap.  XIX,  189 
acids  of     .     .    .     .    Chap.  XX,  204 

allotropic  forma 194 

amorphous 194 

dioxide 204 

bleaching  by 208 

preparation  of 204 

properties,  chemical  .    .     .  206 

physical 206 

uses      .......'.  208 

extraction,  Frasch  method      .  189 

Sicilian  method     ....  191 

flowers 191 

forms  of 192 

milk  of 194 

native 189 

occurrence 189 

oxides Chap.  XX,  204 

plastic 194 

prismatic 193 

properties 195 

purification 191 

resemblance  to  other  elements  196 

roll 192 

springs 200 

trioxide 210 

preparation 209 

properties 209 

uses       197 

Sulphuric  acid 210 

preparation,  chamber  process  212 

contact  process      ....  210 

properties,  chemical  ....  215 

physical 215 

uses 217 

Sulphuric  anhydride      ...  210 

Superphosphate  of  lime    .     .  340 

Supersaturation  in  solutions  55 

Symbols,  meaning  of   ....  102 


of  elements,  table  of  ...  506 

Sympathetic  ink 447 

Synthesis,  definition  ....  43 

as  type  action 118 

Tallow,  beef 486 

Tannic  acid 379 

Tartaric  acid 484 

Tellurium 404 

Temperature,  correction  for    .  14 

Tempering-  of  steel     ....  371 

definition  of       374 

Ternary  compounds  ....  110 
Tests,  insoluble  substances  used 

as 164 

Thermit  process 415 

Thomas   and  Gilchrist   pro- 
cess        366 

Thomas  slag .  366 

Thorium  series   .    .    .    .    .    .499 

Tiles 420 

Tin Chap.  XXXV,  428 

alloys  of 430 

block 428 

chlorides 430 

compounds  of 430 

crystals 430 

foil 430 

metallurgy  of 428 

occurrence  of 428 

oxide 428 

properties  of 428 

sulphide 431 

uses 429 

Tintypes 403 

Tinware  . 430 

Trichlormethane 478 

Tri-iodomethane 478 

Tungsten  steel 369 

Turnbull's  blue  .......  380 

Tuyeres 360 

Type  metal 434 

Umber,  burnt 376 

raw 376 

Uranium  series  ......  498 

Valence,  change  by  oxidation 

and  reduction  ....  378 

definition 108 


526 


INDEX 


References 

Valence  —  Continued 

of  elements,  table  of      ...  506 
relation  to  charges  carried  by 

ions 156 

Vanadium  steel 369 

van't  Hoff,   Jacobus  Henri- 

cus,  portrait    .  facing  152 

Vapor  density 96 

Vaporization,  heat  of  ....  50 

Vaseline 465 

Venetian  red 376 

Vermilion 353 

Vichy 310 

Vinegar 484,  467 

quick  process  for 467 

Vitriol,  blue 392 

green 379 

oil  of 215 

Volatile  compounds,  table  of  509 
Volatility,  reactions  that  go  to 

an  end  through     .     .     .  162 


Washing-  soda 181 

Water  and  solution  .  Chap.  VI,  50 
Water,  composition  of    Chap.  V,    43 

distillation  of 51 

electrolysis  of 33 

hard 309 

action  with  soap   ....    486 

permanent 309 

temporary 309 

of  crystallization  ....     57,  61 

definition 61 

properties,  physical   ....      50 

purification  of 51 

by  aluminum  hydroxide     .    418 
by  copper  sulphate    .     .     .    393 

by  distillation 61 

by  ozone 29 

synthesis,  gravimetric    ...      44 

volumetric 43 

Water  gas 313 

enriching  of 313 

Water  glass 321 

Water  vapor,  correction  for     .      17 

in  air 226 

pressure  of,  table  of  .     .     .21,  510 


are  to  pages. 
Weight  change  on  heating 

metals  in  air      ...  3 
Weights,  combining     .    Chap.  V,  43 

Welding 365 

Welsbach  burner 302 

Whisky 467 

White  lead 435 

Dutch  process  for 435 

White  metal 430 

Wine 467 

Wood,  decaying  of 25 

destructive  distillation  of  .     .  462 

Wood  alcohol     ......  480 

production  of 462 

Wood's  metal 265 

Wrought  iron 365 

composition 365 

manufacture  of 364 

properties 365 

uses.     .                                        .  365 


Xenon 


229 


Yeast 465 

Yellow  prussiate  of  potash  .  379 

Zinc      .     .     .    Chap.  XXIX,  343,  345 

alloys 348 

blende 345 

chloride 349 

dust 346 

extraction 345 

granulated 346 

hydroxide 318 

ingot 346 

ores 345 

oxide 348 

properties,  chemical  ....  347 

physical    .,.:...  346 

purification 346 

sheet 346 

spelter 346 

sulphate    ........  349 

sulphide    .     .     ' 349 

tests  for,  in  compounds       .     .  348 

uses.     .........  348 

Zincite 345 

Zymase 465 


T2J«tt'52LtJ 
DEAD 

4Hay'54MC 


date  stamped  below. 


6925 


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